Dynamic Message Signs - Direct Traffic · Book 10 • Dynamic Message Signs 6 Ontario Traffic...

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Ontario Traffic Manual • December 2007 1

Book 10 • Dynamic Message Signs

OntarioTraffic Manual

Foreword

The purpose of the Ontario Traffic Manual (OTM)is to provide information and guidance fortransportation practitioners and to promoteuniformity of treatment in the design, application andoperation of traffic control devices and systemsacross Ontario. Further purposes of the OTM are toprovide a set of guidelines consistent with the intentof the Highway Traffic Act and to provide a basis forroad authorities to generate or update their ownguidelines and standards.

The OTM is made up of a number of Books, whichare being generated over a period of time, and forwhich a process of continuous updating is planned.Through the updating process, it is proposed that theOTM will become more comprehensive andrepresentative by including many traffic controldevices and applications specific to municipal use.Some of the Books of the OTM are new, while othersincorporate updated material from the OntarioManual of Uniform Traffic Control Devices (MUTCD)and the King’s Highway Guide Signing PolicyManual (KHGSPM).

The Ontario Traffic Manual is directed to its primaryusers, traffic practitioners. The OTM incorporatescurrent best practices in the Province of Ontario. Theinterpretations, recommendations and guidelines inthe Ontario Traffic Manual are intended to providean understanding of traffic operations and theycover a broad range of traffic situations encounteredin practice. They are based on many factors whichmay determine the specific design and operationaleffectiveness of traffic control systems. However, nomanual can cover all contingencies or all casesencountered in the field. Therefore, field experienceand knowledge of application are essential indeciding what to do in the absence of specificdirection from the Manual itself and in overriding anyrecommendations in this Manual.

The traffic practitioner’s fundamental responsibility isto exercise engineering judgement and experienceon technical matters in the best interests of thepublic and workers. Guidelines are provided in theOTM to assist in making those judgements, but theyshould not be used as a substitute for judgement.

Design, application and operational guidelines andprocedures should be used with judicious care andproper consideration of the prevailingcircumstances. In some designs, applications, oroperational features, the traffic practitioner’sjudgement is to meet or exceed a guideline while inothers a guideline might not be met for soundreasons, such as space availability, yet still produce adesign or operation which may be judged to be safe.Every effort should be made to stay as close to theguidelines as possible in situations like these, todocument reasons for departures from them, and tomaintain consistency of design so as not to violatedriver expectations.

Custodial Office

Inquiries about amendments, suggestions or commentsregarding the Ontario Traffic Manual may be directed to:

Ontario Traffic Manual CommitteeMinistry of Transportation OntarioTraffic Office301 St. Paul Street, 2nd FloorSt. Catharines, OntarioL2R 7R4

Telephone: (905) 704-2960Fax: (905) 704-2888E-mail: [email protected]

A user response form is provided at the end of Book 1.Inquiries regarding the purchase and distribution of theOTM Books and the Master Sign Library (MSL) may bedirected to the custodial office identified above, or tothe OTM Committee’s current publishing agent.

Inquiries specific to Book 10 (Dynamic Message Signs)can be directed to the Lead Office for this book asshown below:

Advanced Traffic Management SectionMinistry of Transportation Ontario1201 Wilson Ave., 6th Floor, Building DDownsview, OntarioM3M 1J8

Telephone: (416) 235-3798Fax: (416) 235-4097E-mail: [email protected]

Book 10 (Dynamic Message Signs) was developed withthe assistance of a Technical Advisory Committeeorganized by the Ministry of Transportation Ontario.

Acknowledgements

Project Consultant Team

Tim Schnarr, Delcan Corporation

Simon Lau, Delcan Corporation

Ron Stewart, IBI Group

Anna Dybka, IBI Group

Maryann Lovicsek, IBI Group

Milton Harmelink, Dillon Consulting Limited

Rodney Edwards, Harpar Management Corporation

Suzanne Rodenkirchen, Green Leaf Communications

Technical Advisory Committee

Ataur Bacchus, ITS Section, Ministry of TransportationOntario

Dave Banks, Transportation Engineering, The RegionalMunicipality of Waterloo

Jim Bell, City of Ottawa and Municipal EngineersAssociation

Wayne Bell, Central Region East, Ministry ofTransportation Ontario

Steve Birmingham, Central Region West, Ministry ofTransportation Ontario

Nick Buczynsky, Traffic Office, Ministry ofTransportation Ontario

Harold Doyle, Traffic Office, Ministry of TransportationOntario

Steve Erwin, ITS Section, Ministry of TransportationOntario

Martin Maguire, Transportation Services, City ofToronto

Philip H. Masters, Advanced Traffic ManagementSection, Ministry of Transportation Ontario

John Proctor, Central Region West, Ministry ofTransportation Ontario

Randy Sanderson, Road Safety & Motor VehicleRegulation, Transport Canada

Lizuarte Simas, Traffic Control Systems, The RegionalMunicipality of York

Felix Tam, Advanced Traffic Management Section,Ministry of Transportation Ontario

Bruce Zvaniga, Transportation Services, City of Toronto


Ontario Traffic Manual • December 20072


Book 10 • Dynamic Message SignsBook 10 • Dynamic Message Signs

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.1 Purpose and Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.2 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2. Planning Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3. Dynamic Message Signs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3.1 Variable Message Signs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3.1.1 Functionality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Discrete Character Matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Line Matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Full Matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Combination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3.1.2 Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Light-Emitting Diode (LED) VMSs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3.1.3 Ontario Experience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3.2 Changeable Message Signs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3.2.1 Functionality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3.2.2 Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Blank-out Sign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Fold-out/Flap Sign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Rotating Drum/Prism Sign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Fixed-Matrix Sign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18


3.3 Portable Variable Message Signs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

3.3.1 Functionality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

3.3.2 Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22




4. Design Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

4.1 Optical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

4.1.1 Colour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

4.1.2 Luminance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

4.1.3 Luminance Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25


4.1.5 Viewing Angle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26


4.2 Display Characteristics and Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

4.2.1 Spacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

4.2.2 Fonts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

4.2.3 Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

4.3 Sign Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

4.4 Sign Placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

4.4.1 Freeway Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

4.4.2 Arterial Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

4.4.3 Queue Warning Signs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

4.4.4 Lane Control Signs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

4.4.5 Portable Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Visibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Roadside Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

4.4.6 Site Safety and Maintenance Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . 35

5. Operational Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

5.1 Message Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36


5.2 Alternate Display Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41


5.3 Message Comprehension and Credibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44


6. Other Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

6.1 Communications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

6.2 Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

6.3 Grounding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

6.4 Mounting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48



6.5 Maintenance Access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

6.6 Material Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Sign Face . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

6.7 Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

7. Addendum – Excerpt from Bilingual Sign Design Study . . . . . . . . . . . . . . . . 50

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

Appendix A • Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Appendix B • References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

List of Tables

Table 1 – Character Spacing for MTO COMPASS Signs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Table 2 – Recommended Character Height Based on Message Contentand Posted Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

List of Figures

Figure 1 – Discrete Character Matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Figure 2 – Line Matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Figure 3 – Full Matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Figure 4 – Combination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Figure 5 – Single LED Cluster . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Figure 6 – MTO Overhead Gantry-mounted VMS Display Format . . . . . . . . . . . . . . . . . . . . 14

Figure 7 – MTO Overhead Gantry-mounted VMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 8 – MTO Roadside-mounted (Cantilever) VMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 9 – MTO Combination Sign for the Queue Warning System . . . . . . . . . . . . . . . . . . 16

Figure 10 – Jarvis Street Lane Control Signs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Figure 11 – Thorold Tunnel Lane Control Signs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Figure 12 – Champlain Bridge Lane Control Signs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Figure 13 – Portable Variable Message Sign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Figure 14 – Roadside Safety Considerations in PVMS Placement . . . . . . . . . . . . . . . . . . . . . 21

Figure 15 – VMS Viewing Angle and Luminance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Figure 16 – MTO Font for Permanent Variable Message Signs . . . . . . . . . . . . . . . . . . . . . . . . 30

Figure 17 – MTO Font for Portable Variable Message Signs . . . . . . . . . . . . . . . . . . . . . . . . . . 31



1. Introduction

1.1 Purpose and Scope

Book 10 (Dynamic Message Signs) is one of aseries of volumes that makes up the Ontario TrafficManual (OTM). Book 10 should be read inconjunction with Book 1 (Introduction to the OntarioTraffic Manual) and its appendices, which containconsiderable information about the fundamentalprinciples and policies behind the design andapplication of traffic control signs, signals, markingsand delineation devices. Applicable Ontarioexperience has also been provided to illustratecurrent practices within the Province of Ontario.

Other books in the OTM series provide practicalguidance on a full range of traffic control devicesand their applications. A complete listing of theplanned and currently available volumes is found inBook 1, and an illustrated master index is found inBook 1a (Illustrated Sign and Signal Display Index).

This Book provides information about the planning,design, installation and operation of DynamicMessage Signs (DMSs) for use in outdoor, trafficmanagement related applications. The informationprovided is by no means exhaustive and agenciesare encouraged to refer to the research reportslisted in the References section at the end of thisbook. Other applications, such as the use of DMSsin bus or rail passenger information systems orother specialized purposes are beyond the scope ofthis Book.

Earlier documents used the term “ChangeableMessage Signs” to encompass all signs that had thecapability to display different messages. However,the term “Dynamic Message Signs” is now used todescribe an array of sign technologies that have thecapability of displaying different messages to suitchanging conditions on the roadway. Included withinthe family of Dynamic Message Signs are full-matrix

displays, single-line or character-matrix displays,multiple pre-set message displays and simple on-offor “blank-out” displays. Although the term“Changeable Message Signs” has in the past beenused in Ontario to describe the full family of signtechnologies, the term “Dynamic Message Signs” isbeing adopted in the OTM to conform with standardterminology being adopted by the Joint Committeeon the National Transportation Communications forITS Protocol (NTCIP). The terms “Variable MessageSigns” and “Changeable Message Signs” are usedin the OTM to describe specific sub-sets of DynamicMessage Signs. The “variable” message sign is atype of sign in which the message to be displayedcan be created and downloaded into a temporarymemory area of the sign controller and displayed onthe sign face. They can display a full array ofmessage combinations. The “changeable” messagesign is a type of sign which can display a smallnumber of predefined messages or a blankmessage. Additional information about the differentsign types and technologies is provided in thefollowing sections of this Book.

The intent of Book 10 is to give sufficientinformation to the reader to ensure that he/she isaware of the key design elements that must beconsidered in the selection and use of DynamicMessage Signs. Typically, such signs are usedwithin the context of a traffic management system.Information about the control systems for DMSs andhow the signs fit within a traffic managementsystem may be found in a companion volume, OTMBook 19 (Advanced Traffic Management Systems).

Portable Variable Message Signs (PVMSs) are oftenimportant for traffic control under temporaryconditions, particularly in construction zones. Forinformation on the application of PVMSs undertemporary conditions, reference must be made toOTM Book 7 (Temporary Conditions).



1.2 Background

The ability to provide real-time or near real-timedynamic messages to motorists facilitates safer andmore efficient use of existing roadways. As a result,motorists can experience less delay, reducedfrustration and a safer environment, whiletransportation agencies can maximize the capacityof existing infrastructure and defer costly capitalexpenditures for infrastructure expansions. DynamicMessage Signs (DMSs) can provide diversioninformation in the event of partial or full closures,can enable network management by providing traveltime and speed information on the different links,and can assist with route planning by notifyingmotorists of scheduled events that may impactroadway operation.

Considerable research work has been done on theeffective design and use of Dynamic Message Signsover the thirty or more years that they have been incommon use in North America, Japan and Europe.Sign technologies have changed. Although newtechnologies will no doubt emerge in the future,research has identified several fundamental factorsthat influence the effectiveness of all sign displays,independent of the technology in use. Thesefundamental factors govern the size, location, displaycharacteristics and message content of DynamicMessage Signs, which are listed below. Within theseguidelines, the most appropriate technology shouldbe chosen to suit the particular combination oftraffic management goals, functional requirementsand available budget.

• Conspicuity – does the sign attract attentiongiven the background in which it is placed?

• Legibility – at what distance can drivers readthe sign?

• Information load – do drivers have sufficient timeto read the entire message without undulydiverting their attention from the driving task?

• Comprehension – do drivers understand themeaning of the message, including any symbolsand abbreviations used?

• Driver response – do drivers make the desiredaction as a result of reading the sign?

Additional information about these factors and howthey affect sign design and the driver’s ability tosafely navigate within the traffic stream may befound in OTM Book 1b (Sign Design Principles) andin OTM Book 2 (Sign Design, Fabrication andPatterns). It should be noted that although the basicdesign principles apply to all signs, some of thespecific information and comments presented inBook 1b are primarily applicable to fixed signing.Some examples include sign colour, shape and fonts,which are generally different for dynamic signs dueto restrictions imposed by the technologies involved.These factors are explored further in Section 4(Design Considerations).



2. Planning Considerations

Dynamic Message Signs (DMSs) are useful in manysituations where traffic operations and safety canbenefit from the ability to advise drivers of changingconditions in real-time or near real-time. They can beused in rural and urban settings on any classificationof road. DMSs can be used for various purposes andcan provide incident management, congestionadvisory, queue advisory, route diversion, generalspeed management, work zone speed management,lane control, parking guidance, travel time advisory,and planned event information.

Dynamic Message Signs are typically implementedas part of an Advanced Traffic Management System(ATMS) and serve as the mechanism for providinginformation to motorists. The link between the DMSsand the ATMS is crucial as the ATMS is responsiblefor collecting the information that will be displayedon the DMS. Therefore, the size, location and type ofDMS is dictated largely by the particular application,including specific messages to be displayed, or thetype of system that it is supporting.

DMS planning is one component of overall planningfor Advanced Traffic Management Systems, asdescribed in Section 3 of OTM Book 19 (AdvancedTraffic Management Systems). In order to makesound decisions on DMS type, technology andquantity, it is necessary to perform the preliminaryplanning steps, including establishing the goals andobjectives to be fulfilled by the specific ATMS andselecting appropriate strategies to be delivered bythe system.

In rural areas, DMSs can play a key safety role inlocations that have a history of road closures due topoor road conditions as a result of weather (heavyfog, ice, drifting snow etc.). When placed in key

locations in advance of these hazard areas, theDMSs can be used to advise motorists of weather-related restrictions so that they can modify theirtravel plans accordingly.

In urban areas, Dynamic Message Signs form anintegral part of freeway or urban arterial ATMSs, atvarying levels of sophistication. For example, theycan be linked to highly automated systems thatcollect various types of traffic information, such astraffic volume, speed and lane occupancy, in whichthe DMSs are used to automatically displaycongestion and travel time advisory messages. Theopposite end of the spectrum is a more manualsystem that requires manual collection ofinformation, selection of appropriate messages andcontrol of the DMS.

Portable Variable Message Signs (PVMSs) can beuseful for providing information or warning to driverswhen temporary conditions are encountered, forexample, where roadway alignment or laneconfiguration is altered during various stages of roadconstruction, during roadway maintenance activities,or during special events. In all cases, thedeployment of these portable devices has to becarefully managed (see Sections 3.3 and 4.4.5).

When the appropriate type of DMS has beenselected to meet the functional requirements of aspecific ATMS, the latter stages of planning need toconsider placement of all DMSs within the physicalconstraints of the applicable roadways (see Section4.4), including freeway, arterial and portableapplications. Placement issues may impact DMSsize and technology. Performance, reliability andmaintenance issues (see Sections 3.1.2, 3.2.2,3.3.2 and 6.5) also need to be considered in DMSplanning, as they impact the DMS technologyselected for the system.



DMSs can be used to support different types ofIntelligent Transportation Systems (ITS) includingCommercial Vehicle Operations (CVO) andAdvanced Public Transit Systems (APTS). Thesetypes of applications for Dynamic Message Signsare considered to be outside the scope of this book.The general guidelines discussed in this book arestill appropriate for these different types ofapplications; however specific details such asmounting and placement will need to be adapted tosuit the application.

3. Dynamic Message Signs

There are several categories of Dynamic MessageSigns (DMSs) available on the market, which will bereferenced in this Book as Variable Message Signs(VMSs), Changeable Message Signs (CMSs) andPortable Variable Message Signs (PVMSs). Eachsign type provides real-time or near real-timeinformation to motorists. The differences betweenthese types of DMSs are determined by: thecapability of the technology, the level of variation inthe messages to be displayed, and the differentlevels of functionality that each type offers.

One of the first steps that an agency must undertakewhen determining which type of DMS to implement,is to develop a good understanding of the trafficmanagement purposes for which the DMS will beused. This includes understanding the length,number and type of messages that will be displayed,as well as the frequency of use. Using thisbackground information, the required functionality ofthe sign can be determined and the appropriate typechosen. Other factors, such as maintenanceconsiderations and price, will also influence theselection of the signs.

The following sections describe the functionality ofeach DMS class, as well as the current technologiesthat are used for each sign type. Once an agencyhas decided on functionality requirements, the mostappropriate technology may be selected.



3.1 Variable Message Signs

3.1.1 Functionality

Variable Message Signs (VMSs) provide the highestlevel of functionality of all of the DMSs and areconsequently also the most expensive. Assuggested by the name, VMSs contain a variabledisplay, made up of a grid or matrix of discrete dots,known as pixels. Using different combinations ofthese discontinuous pixels, the sign appears to thehuman eye as if the display is actually a continuousformed character or graphic symbol. VMSs candisplay a full array of characters and spaces to formvirtually any message combination and can alsohave full graphics capability.

VMSs are particularly effective tools for providingmotorist information in an environment thatexperiences continuous and rapid change. Theflexibility in message combinations and graphicsensures that the VMSs are capable of displaying anytype of information. The VMSs are fully configurableand can be designed to meet an agency’s specificrequirements. This includes the number of lines aswell as the number of characters per line.

There are three different classes of VMS, listed inascending levels of functionality: Discrete CharacterMatrix; Line Matrix; and Full Matrix.

As the functionality increases so does the cost ofthe sign. However, greater functionality allows moreflexibility in displaying content and improveslegibility.

These different classes of VMSs can also becombined to form a combination sign. Thiscombination sign can provide the appropriate levelof flexibility at a reduced cost. From a functionalstandpoint, full-matrix or combination signs arepreferred.

Discrete Character Matrix

A discrete character matrix sign has a display boardcontaining an individual display module for eachcharacter, as illustrated in Figure 1. Characters areseparated by a blank space. Each display modulecan display a full array of characters but only simplegraphics, because the size of the graphic is limitedto the size of the module. This limitation means thatonly simple graphics such as arrows can bedisplayed. The font is also restricted to charactersthat fit the size of the matrix, resulting in someletters, such as “X” or “W”, being compressed. Thediscrete character matrix is the most economicaltype of VMS, however, the use of discrete charactermatrix signs has largely been eliminated in favour ofmore flexible designs.

Figure 1 – Discrete Character Matrix



Line Matrix

A line-matrix sign has full-matrix capabilities alongeach line of standard character height and candisplay a full array of characters along that line, asillustrated in Figure 2. Typically, such a VMS will bemade up of two or three lines. The line-matrix signoften has limited graphics capabilities as the heightof the graphic is physically restricted by the heightof the line. Also, if French language accents arerequired, a reduced height letter must be used toaccommodate the letter and accent within the lineheight. The legibility of the line-matrix sign is betterthan the discrete character matrix sign becausethe characters can be fully formed and the fonts canbe configurable, allowing for proportional spacing.Proportional spacing is discussed further inSection 4.2.2.

Full Matrix

A full-matrix sign offers the most flexibility of all ofthe VMSs. As Figure 3 indicates, the entire area ofthe sign face can be used for display; and can bedivided into lines to display text messages, or used inits entirety to display full graphics, or broken intosections of text and graphics. These signs also allowfor variation in the height of characters used formessages, e.g., French language accents over full-height letters are supported. The full-matrix signs arethe most expensive type of sign.

Combination

Combination signs integrate the different types ofsigns into one sign, depending on the functionalityrequired for the different areas of the sign. Forexample, a full-matrix area could be provided oneither end with line matrices in between, asillustrated in Figure 4. Combination signs can also

Figure 2 – Line Matrix

Figure 3 – Full Matrix



be made up of both static and dynamic components.The advantage of combination signs is that theyoptimize functionality at a reduced cost. Thedisadvantage is reduced display flexibility, i.e., aparticular sign configuration may not be ideallysuited for applications such as French languageaccents over full-height letters.

3.1.2 Technology

There are various Variable Message Signtechnologies available on the market, which havebeen developed over a period of time for use indifferent environments, e.g., roadway, advertising,pedestrian, indoor use and sporting arenas. Some ofthe technologies can be used in all environments,while other technologies, such as neon lighting, arebest suited for non-traffic applications. Technologiessuch as incandescent bulb matrix and fluorescentflip-disc technology have been used in the past forDMSs and may still exist in some jurisdictions, butnew installations are not recommended due to highoperating and maintenance costs and the superiorperformance of alternative products.

The technologies described below have been testedand used successfully in roadway environments.Alternative technologies to this list could beconsidered, but the transportation agency mustensure that the visual requirements discussed in

Sections 4.1 and 4.2 have been met and tested andthat the technology can deliver the requiredfunctionality. Consideration should also be given toon-going operating and maintenance costs.

Light-emitting signs are now considered to be theonly acceptable option for VMSs, as they provide thebest visibility to motorists under different lightingconditions. There are three basic types of light-emitting signs in common use worldwide, withvarying degrees of performance and reliability: light-emitting diode (LED), fibre optic, and hybrid signs.Fibre optic signs are the oldest of the three signtechnologies and currently have limited availability inthe North American market. Hybrid signs areconsidered to be obsolete. LED technology iscurrently the only viable VMS technology. Continuingavailability of particular sign models of anytechnology can be uncertain, due to a particularlyvolatile supply industry.

Light-Emitting Diode (LED) VMSs

Light-emitting diode or LED VMSs are currently thepreferred type of light-emitting sign technology. Thepixels for LED signs are comprised of multiple light-emitting diodes, which are solid state electronicdevices that glow when a voltage is applied. Varioustechniques are available to adjust the luminance ofthe sign to ambient light conditions.

Figure 4 – Combination



Individual pixels are typically comprised of multiplestrings of LEDs connected so that if one string failsthe other strings will still emit light, reducing the riskof a total pixel failure. LEDs have a very highreliability with over 150,000 hours of continuousoperation expected. The low power requirementscoupled with the long life and high reliability haveresulted in the LED VMSs becoming the mostpopular type of light-emitting VMS.

Some earlier examples of LED signs had pixels madeup of a combination of red and green LEDs to givean amber colour display. However, the differentcolour LEDs did not age at the same rate, causingcolour shifts and loss of colour uniformity across thesign. In subsequent development, LEDmanufacturers designed and produced high-intensityyellow/amber LEDs with an emitted lightwavelength of 590 nanometres (nm), which hasbecome the de facto standard output for VMSs intraffic applications. Signs are now available with asfew as four high-intensity LEDs per pixel, focussedthrough a special lens. Recently, a white LED hasbeen developed, which is now available in signs

from at least one VMS manufacturer; however,there is as yet no long-term experience with theseLEDs. Figure 5 illustrates a single pixel from aLED-type VMS.

Full-matrix LED signs sometimes use pixels of red,green and blue LEDs to generate the full spectrumof colours. While these signs have been used mainlyas scoreboard displays in stadiums and as billboardadvertisements in North America, there are a fewexamples of their use in transportation applicationsin South America. These signs are expensive,making them an unlikely technology for widespreadtransportation applications in North America.

It can be expected that continuous improvementswill be made to LED technology, resulting inchanging price and performance characteristics. Itwill therefore be important to monitor how well theVMS manufacturers incorporate these developmentsinto their products.

Figure 5 – Single LED Cluster



3.1.3 Ontario Experience

The Ministry of Transportation Ontario hasimplemented several types of VMSs with varyinglevels of functionality over the past 25 years,including discrete character matrix signs, line-matrixsigns and combination signs. Technologies haveincluded fluorescent flip-disk, fibre optic flip-disk andLED signs. All of the original fluorescent flip-discsigns were replaced a number of years ago. MTOhas been very active in the development of LEDdisplays since 1989, and the current MTO approachis to deploy only LED-based VMSs. The fewremaining fibre optic flip-disk signs are scheduled forreplacement in the near future. Early generation LEDdisplays utilized pixels which combined red andgreen LEDs to achieve the desired amber colour.

Over time the LEDs tended to degrade at varyingrates contributing to non-uniform discolouration andlight output. These early generation displays havesince been upgraded to current high-output amberLED pixels.

The Ministry’s current standard for overhead gantry-mounted VMSs is a combination sign as illustratedin Figure 6. The display contains a full-matrixgraphics display element at each end of the signface, comprised of display modules (each with 35pixels in a 5 x 7 matrix) arranged in five horizontalrows and seven vertical columns giving a 35 x 35pixel display. Between these two full graphics panelsis a three line matrix, each line comprised of 21display modules, giving a 105 x 7 pixel display.

Figure 6 – MTO Overhead Gantry-mounted VMS Display Format



MTO originally developed the combination sign forimplementation throughout the Highway 401corridor in order to be able to display full graphics,such as exit arrows and highway identificationshields, on either end of the sign. Through themiddle section of the sign, text messages aredisplayed to motorists and therefore the fullfunctionality of a full-matrix sign is not required. Linematrices were specified instead in order to reducecost. Figure 7 depicts a MTO overhead gantry-mounted VMS on Highway 401, Toronto.

A different VMS configuration is used on undividedhighways and freeways where there are two or lesslanes per direction. Figure 8 shows an example of aroadside-mounted (cantilever) VMS located on

Highway 69. The VMS is full matrix in its entirety,and is 105 pixels wide by 30 pixels high. Three linesof text can be displayed on the VMS, and the displaywidth is about 60% that of the standard MTOoverhead gantry-mounted VMS illustrated inFigure 6.

Different VMS designs have resulted not only fromtechnological advances, but also from variations inthe intended function of the display and the locationof the sign being installed.

MTO has implemented combination signs for theQueue Warning System on the Queen Elizabeth Wayin Fort Erie, on Highway 405 in Niagara Falls, andHighway 402 in Sarnia. The signs consist of a static

Figure 7 – MTO Overhead Gantry-mounted VMS



sign, amber flashers, and a single line-matrix LEDVMS. Figure 9 depicts an MTO combination sign forthe Queue Warning System.

When procuring VMSs, several months lead timeare usually required for delivery, as each order iscustom made to suit the needs of the purchaser.VMSs are not generally commercially available asoff-the-shelf items.

Figure 8 – MTO Roadside-mounted (Cantilever) VMS

Figure 9 – MTO Combination Signfor the Queue Warning System



3.2 Changeable Message Signs

3.2.1 Functionality

The class of Dynamic Message Signs known asChangeable Message Signs (CMSs) also providesdynamic information to motorists; however, only alimited number of messages can be displayed. Themessages are pre-defined and, unlike on VMSs,cannot be individually configured. One type of CMSis known as a Blank-out Sign.

Blank-out signs have two states, either on or off.When the Blank-out Sign is off, no message isdisplayed. When the sign is on, a pre-determinedmessage is displayed to motorists. This type of signis effective in situations where the agency wishes toadvise motorists that a particular condition eitherexists or does not exist. Examples might include aramp, road or bridge closure or turn restrictions thatonly apply at certain times of the day. When theBlank-out Sign is in its default state (off), themotorist can assume that the condition is notpresent.

Pre-set message signs are capable of displaying oneof several static messages to motorists. The specificmessages available are fixed, but there is flexibility inwhich message to display. This type of CMS isuseful in providing, for example, information onlevels of congestion or alternate routes to majorattractions.

3.2.2 Technology

There are several different types of CMStechnologies on the market. In Ontario, the typesthat are used include the light-emitting Blank-outSign, the Fold-out or Flap Sign, the Rotating Drum/Prism Sign, and the Fixed-matrix Sign.

Blank-out Sign

The Blank-out Sign is a light-emitting sign that onlyhas two phases: either on or off. The technologyused for these signs includes:

• Formed neon-type clear glass tubing on a paintedbackground;

• Fluorescent lamps behind a cut out legend;

• Fibre optics in a fixed pattern; or

• LEDs in a fixed pattern.

When the CMS is on, the fixed message isilluminated. Otherwise, no message is displayed.Depending on the level of system automationdesired, the signs can be operated either manually,whereby an operator is responsible for activating amessage, or automatically, whereby if a particularcondition is met, the sign message is automaticallydisplayed.

These technologies have a reasonably goodmaintenance experience because there are fewmoving parts. The neon and fluorescent types mayhave some difficulty in start-up during very coldweather.

Fold-out/Flap Sign

The Fold-out/Flap Sign is a non-light-emitting sign. Itis a conventional-looking highway sign that has ahinged or louvered viewing face, generally operatedby a motor. When the hinged face is open, motoristscan view the front of the sign face and see a typicalstandard static sign. When closed, only the backside of the hinged section is visible. These signs canbe used very effectively at intersections where rightor left turns are only permitted during certain periodsof the day and also to support transit applicationswhere motorists are allowed to enter a transit rightof way only during off-peak hours. As the signs aremade from the same material as static signs, they



are identical in look and can easily conform to theregulatory requirements. The design of the legendfor these signs must be in conformance with thestandards for highway signs. See OTM Book 2 (SignDesign, Fabrication and Patterns).

Fold-out/Flap Signs have been known to experiencesignificant maintenance problems due to theexposure of moving parts to the environment.

Rotating Drum/Prism Sign

The Rotating Drum/Prism sign is a non-light-emitting sign. Typically, the viewing face is similar inappearance to that of the conventional highwaysign. Designs used to form the message includeraised sheet metal letters on a painted aluminumbackground, spray masked lettering on paintedaluminum sheeting, reflective sign sheeting ortranslucent plastic background. Rotating Drum/Prism Signs typically have two or more activemessages and a default or blank state that can bedisplayed to the motorist. Messages are displayedby rotating the drums to the appropriate viewingposition. Each drum typically has three to six facesto display different messages. The overall numberand combinations of messages that can bedisplayed increases with the number of drums usedfor each sign. As a result, rotating drum signs havethe highest functionality of all the CMSs. Rotatingdrum signs are relatively inexpensive to operate andmaintain, however, the moving parts such as motorsand drive mechanisms and drum position switchesare susceptible to wear and damage. Winterweather conditions can cause snow and ice build-up, which can restrict or prohibit movement of thesign panels. For these reasons, the rotating drum/prism is not recommended as a CMS technology.

Fixed-matrix Sign

With this type of sign a message is created on thesign by arranging LEDs or fibre optics on the signface to make up the desired message. Additionalmessages are created on the sign face in the same

way. The desired message is displayed by turningon only the LEDs or fibres for that message. Acommon example of this type of sign is thepedestrian walk/don’t walk signals used at manytraffic signal installations where both messages aredisplayed on the same sign face.

The number of messages is limited by the space onthe sign face. Generally only a few messages will fit.


The City of Toronto uses lane control signs tooperate the reversible lane on Jarvis Street. Theselane control signs consist of LED lane controlmodules. They are primarily installed as pairs ofsingle heads (back to back, facing oppositedirections). A typical lane control sign installation onJarvis Street in the City of Toronto is shown inFigure 10.

The City of Toronto uses mechanical louvered signsto display turn restrictions by time of day, generallycontrolled through an output from the traffic signalcontroller. These mechanical signs typically requiretwo to three preventive maintenance visits per year.The signs seize (stop moving) from time to time,

Figure 10 – Jarvis Street Lane Control Signs



requiring immediate maintenance. Any lack ofreliability causes concern over the enforcement ofturn restrictions at locations with mechanical signs.

The Thorold Tunnel on Highway 58, which crossesunder the Welland Canal, incorporates a lane controlsystem for traffic control during normal operationsand during maintenance or emergency situationswithin the tunnel. The dual tube tunnel has two lanesin each direction. Lane control signs are mounted atthe ceiling of the entrance and exit portals andthroughout the tunnel, to show that the lane is eitheropen (green arrow), or closed (red “X”). Figure 11shows the Thorold Tunnel lane control signs.

The Champlain Bridge is a three-lane structurespanning the Ottawa River between Ottawa, Ontarioand Gatineau, Quebec. The centre lane is reversible,and functions as an HOV (High Occupancy Vehicle)lane for buses, taxis and vehicles with two or moreoccupants. The reversible traffic flow is governed bypeak-hour traffic volumes. Hours of priority operationare midnight to noon (flow from Gatineau to Ottawa)

Figure 11 – Thorold Tunnel Lane Control Signs

Figure 12 – Champlain BridgeLane Control Signs

and noon to midnight (flow from Ottawa toGatineau). Overhead, double-sided, lane-control signsdisplaying either a downward green arrow or red “X”indicate the lanes available for each traffic direction.The overhead signs are supplemented by side-mounted blank-out signs, activated only for thestream including the HOV lane. The ChamplainBridge lane control sign system is shown inFigure 12.

In work zones, the MTO has started to installradar-linked Portable Variable Speed Display Signsthat display the speed of an approaching vehicle.The display elements are light-emitting diode (LED)technology, and the sign is capable of displayingspeeds from 0 to 140 km/h (i.e., 3 digits). Theactive sign display is a minimum of 200 mm highand should be clearly legible from any part of theapproach lanes from distances between 45 m and200 m.



3.3 Portable Variable Message Signs

3.3.1 Functionality

Portable Variable Message Signs (PVMSs) typicallyhave the same functionality and basic design asfixed-location Variable Message Signs and arecomprised of discrete characters or full-matrixarrangements. They should meet the same opticalrequirements as the other light-emitting DMSs andare subject to the same character heightrequirements. Full-matrix PVMSs provide moredisplay flexibility than discrete character matrixsigns. The primary difference between PVMSs andregular, fixed VMSs is their smaller size and hencereduced message display capability. It is possible touse CMSs in a portable configuration, however, thelimited display capability is not well suited for use ina temporary environment.

Portable Variable Message Signs should only beused for situations where the conditions arechanging. In general PVMSs could be used in thefollowing conditions:

• Advanced notification of closures due toconstruction. The notification period should notexceed 9 days.

• Advanced notification of major special eventsimpacting traffic. The notification period shouldnot exceed 9 days.

• Notification of initiation of long-term changes inroad configuration (e.g., lane closures, laneopenings, HOV lane openings, etc.).

• Temporary notification of long-term conditions inthe interim until static signs can be manufactured.A PVMS may be used for up to one week while astatic sign is being manufactured.

• Notification of a construction zone and/or areduced speed limit.

PVMSs help alleviate congestion by providingadvance warning of unusual conditions ahead,providing the motorist the opportunity to alter travelplans. Figure 13 depicts a PVMS providing advancewarning of a lane closure.

PVMSs should never be used for advertising anevent. Their use should be limited to the display oftraffic-related information only.

PVMSs have to be easily moveable and placedwhere they can be readily seen from the roadwaywithout compromising public safety. The signsshould, where possible, be placed in an area withexisting barrier protection. If this is not possible, theymust be located a sufficient distance away frommoving traffic so as not to introduce a hazard tomotorists. Figure 14 provides the logic to befollowed when determining the appropriate locationand protection for a PVMS. Substantial additionalinformation about the application of PVMSs intemporary situations may be found in OTM Book 7(Temporary Conditions). In no case should a PVMSbe considered in a roadway work zone withoutreference to Book 7.

Figure 13 – Portable Variable Message Sign



The relatively small size of PVMSs can severelyrestrict the length of message that can be displayed.Care must therefore be taken to ensure that themessage is simple, clear and readily understood.Two-phase messages can be used to expand themessage display capability of the signs.

Where PVMSs are introduced into an area alreadycontaining permanent VMSs operated as part of anATMS, care must be taken to ensure that the twosigns are operated in a co-ordinated manner, so thatthe message on one sign does not conflict with theother, or with the actual traffic conditions on theroad. The dynamic nature of the signs leads thepublic to believe that the information displayed isupdated regularly, and considerable loss of credibilitycan result if two signs display conflictinginformation.

Figure 14 – Roadside Safety Considerations in PVMS Placement

Other issues to be resolved when using PVMSsinclude securing reliable power supply and datacommunications, as well as security againstvandalism. Because they are portable and are oftenoperated at remote sites, the majority of signs usebatteries that are recharged, either by solar panels ordiesel generators. Consequently, some signs maynot operate continuously over a 24-hour periodwithout periodic inspection. Additional informationrelating to power supply can be found in Section6.2. Communications to temporary sites can also bea challenge if the intent is to change messageswithout requiring a site visit. Security issues alsoarise with PVMSs: wheels and towing devicesshould always be removed to prevent theft, andvandal-proof locks should be installed on all controls.



Useful guidelines and cautions for the deployment ofPVMSs include:

• The use of the signs on a 24-hour daily basisrequires careful management to prevent drainingthe batteries;

• Retro-reflective display borders help to improveconspicuity;

• Finding safe mounting locations with goodvisibility can be a challenge on urban freeways, asthe signs will frequently not fit on the availableshoulder area;

• Wherever possible, the signs should be controlledcentrally by the road authority.

3.3.2 Technology

See Section 3.1.2 for a description of the differenttypes of technology that can be used for PVMSs.Due to power supply limitations and fewer movingparts, PVMSs using LED technology provide a moreviable and robust sign than other types of light-emitting technologies. LED is the only technologycurrently allowed on Provincial Highways.


PVMSs are used by the Ministry of TransportationOntario as well as numerous municipalities acrossOntario for a variety of traffic applications, the mostpopular being to support construction work zones orto help manage scheduled events that draw largecrowds.

There are essentially three types of PVMSs approvedfor use on the provincial highway network:trailer-mounted temporary, trailer-mounted semi-permanent, and pole-mounted PVMSs.

There are several methods of obtaining the requiredPVMSs:

(1) MTO regions purchase a fleet of signs througha stand-alone contract,

(2) Contractor purchases PVMSs as part of aconstruction contract; PVMSs would be ownedby MTO at the completion of the contract, or

(3) Contractor provides his own or rented PVMSsfor the duration of the contract.

The MTO prefers to procure PVMSs through a stand-alone contract which includes a provision formovement of the signs. This provides the MTOflexibility in the location of the signs as well as theiroperation, with messaging typically controlledthrough a local COMPASS operations centre. TheMTO is moving forward with deployment of fleets ofPVMSs, with GPS tracking, and NTCIPcommunication protocol.



4. Design Considerations

There are five important factors to be considered inthe planning, design and selection of DMSs toensure their successful application. The descriptionof these factors also applies to PVMSs, exceptwhere noted otherwise. The five factors include:

(1) Conspicuity – does the sign attract attention,given the background in which it is placed?This is a function of both sign technology anddesign as well as the physical environment.

(2) Legibility – at what distance can drivers readthe sign? Legibility depends on characterheight, font style and spacing, contrast ratio,the spacing of characters, words and lines andthe aiming of the sign.

(3) Information load – do drivers have sufficienttime to read the entire message?

(4) Comprehension – do drivers understand themeaning of the message, including anysymbols and abbreviations used? Consistentmessage information is required, particularlyfor geographic descriptions, abbreviations andamount of information presented.

(5) Driver response – do drivers make thedesired action as a result of reading the sign?To respond appropriately, drivers must haveadequate time (distance) to respond to themessage. This will depend on the location ofthe DMSs relative to routing decision points.

An additional issue, especially for DMSs providinginformation in real time or near real time, iscredibility of information, that is, whether driverscan rely on the information displayed. This willdepend on how the source information is obtained,the timeliness of information updates and how wellthe system is managed and operated.

This section addresses the physical design andmessage composition issues that relate to theconspicuity, legibility and comprehension of DynamicMessage Signs. An agency can help ensure thesuccessful implementation of DMSs by reviewing,understanding and implementing the followingdesign considerations.

In practice, many variables must be considered inDMS application:

• traffic often travels in excess of the posted speedin uncongested conditions;

• sign visibility is frequently impaired by weatherconditions or the presence of large trucks;

• a significant segment of the driving populationdoes not have 20/20 vision;

• there continues to be an increasing number ofaging drivers, some of whom experience poornight vision.

Whenever there is any doubt, design standardsshould always be raised rather than lowered.

4.1 Optical Characteristics

It is important to establish minimum opticalperformance characteristics for DMSs to ensureconsistent visibility under various applications andenvironmental conditions. The objective is toconsistently achieve:

• Visibility at 300 m for high-speed arterial road orfreeway applications;

• Visibility at 200 m for lower-speed applications(Dudek).



The parameters used to define the opticalperformance characteristics vary, depending onwhether the DMS is light emitting or non-lightemitting. Book 1b (Sign Design Principles) and Book2 (Sign Design, Fabrication and Patterns) apply toall types of non-light-emitting signs, whether they areDMSs or static signs. Therefore, for non-light-emitting signs, the guidelines detailed in Book 1band Book 2 should be followed.

The parameters used to establish opticalcharacteristics for light-emitting signs are colour,luminance, contrast ratio, and viewing angle. Therehave been numerous technical reports andspecifications prepared around the world thatprovide significant detail about each of theperformance requirements. Detailed technicalspecifications are beyond the scope of this Book.Any agency that is contemplating installing a light-emitting DMS should refer directly to thesedocuments and specifications for assistance indetermining requirements. Examples of currentspecifications include:

(1) Ministry of Transportation Ontario SpecialProvision 685S01 – Changeable MessageSigns; and

(2) Highways Agency UK Specification TR2136(Issue B) – Optical Performance FunctionalSpecification for Discontinuous VariableMessage Signs. This Specification has alsobeing adopted as the European standard,

The optical characteristics described below weredeveloped for permanent overhead VMSapplications. It is intended that they also apply toPVMS applications.

4.1.1 Colour

Several colours can be displayed on DMSs,depending on the technology that is utilized: amber,white, red, green and blue. The most visible of thesecolours, and the most commonly used for textmessages, is amber or white. The choice of colouris often limited by the technology chosen. Untilrecently, LED-based DMSs were unable to displaywhite light, therefore amber became the preferredcolour, with a nominal wavelength of 590 ±5nanometres. White LEDs have not yet been widelyused in transportation applications, so experience todate is limited.

Colours other than white or amber are notcommonly used, due to their lower contrast values.One exception is when the DMS must displayregulatory information and red is introduced into theDMS, usually on non-light-emitting signs only.

Regardless of which type of technology is used, thecolour of all pixels should be uniform across thedisplay.

4.1.2 Luminance

The light output of the sign, or luminance, ismeasured in candelas per square metre (cd/m2).Each DMS should be capable of achieving aluminance of 10,000 cd/m2. This typically equatesto a luminance of not less than 40 candela (cd) perpixel at the brightest level for a full 5 x 7 matrix ofamber or white DMS pixels, with all pixels activatedat their maximum design output.

Colours other than amber or white should not beused, as the maximum achievable luminance forother colours is approximately 50% or less lowerthan white or amber. Consequently, it may not bepossible to achieve the desired luminance, makingthe DMS difficult for motorists to see under certainconditions.



PVMSs using solar power are now capable ofmeeting the luminance output requirements.

There must be a mechanism for the luminance to becontrolled both automatically and manually,depending on the ambient light level, in order toprovide the best visibility for motorists. During thebrightest period of the day, and particularly withdirect sunlight on the sign face, the DMS will beoperating at the high end of the luminance range.During the night, the DMS will operate at the lowend of the luminance range, otherwise the DMSwould cause considerable glare to the motorist.Unless the DMS is operated in manual mode, thecontroller is responsible for assigning the luminance.It should be capable of assigning a pixel outputwithin a range of 1 cd to 40 cd, depending on theambient light characteristics, as measured by anappropriately designed photo sensor array on thedisplay.

The readings from the photo sensor array should beaveraged over a suitable period of time,approximately 30 to 60 seconds, so that the DMSintensity is unaffected by transitory changes inexternal illumination, such as passing clouds.

4.1.3 Luminance Ratio

Rather than the pure luminance output of a sign, it isactually the contrast between the legend (i.e., text,symbol, border) and the background of the signwhich provides the legibility of the message to thedriver. This characteristic is known as the LuminanceRatio. The VMS must provide a suitable level ofcontrast between activated and non-activated areasof the display in order to provide the necessarylegibility. The luminance ratio for light-emitting signsdefined in the current MTO specifications is 10 to 1for permanent VMSs (both overhead gantry- and

roadside-mounted) and 6 to 1 for PVMSs withexternal illuminance ranging from 400 lux to40,000 lux. This requirement is consistent with thecurrent European standard.

At the lower ambient light levels, the contrast ratiobecomes less critical for light-emitting signs than forreflective signs. (Ref. CEN/TC 226 EN 12966-1.)

The luminance ratio is tested under laboratoryconditions utilizing a standard methodology and iscalculated as follows:

Luminance Ratio = (La – Lb) ÷ Lb

Where:La = The measured luminance (cd/m2) of the

element in the ON-state.

Lb = The measured luminance (cd/m2) of theelement in the OFF-state.

The luminance output of LEDs, and hence thecontrast, typically degrades over time. Therefore,VMSs using this type of technology should bedeveloped to compensate for this loss in luminance.VMSs should be specified for the LEDs to bepowered at less than 100% of the maximum outputwhen new. Then, as the LEDs age, the power outputcan be increased, thereby maintaining the requiredluminance level. Running the sign at less thanmaximum output will also prolong the life ofthe LEDs.

Care must be taken to maintain contrast ratio andlegibility, which can be adversely affected by directsunlight. To overcome these problems it has beennecessary to screen LEDs with sunvisors, louversand blinds. For example, a 52 mm diameter pixelhas to be set back into a sun visor about 200 mm toprotect the LED from sunlight.




Experience to date in Ontario with both the City ofToronto and the Ministry of Transportation Ontariohas been to use a black matte background materialbehind a non-glare polycarbonate sheet. Thiscombination with the amber/white light providesvery good contrast and enhances the legibility ofthe DMS.

The MTO has also introduced a 75 mm wide strip offluorescent retro-reflective chartreuse or strongyellow-green sign material as a border around theperimeter of the sign case to enhance theconspicuity of the sign, making it stand out betteragainst an ambient background, particularly at night.This is consistent with accepted practice in staticsigns.

4.1.5 Viewing Angle

With light-emitting signs, the angle at which thesign is viewed is very important, due to theproperties of the light sources. As light travels in astraight line with minimal dispersion, there is arelatively narrow cone of vision where the light canbe viewed at full intensity. This is a particularlysignificant property of LED-based signs. As a result,the alignment of the signs becomes an importantissue, to ensure that the message is not truncatedfor the observer at more extreme viewing angles andmotorists can view the message at the highestpossible luminance value.

The viewing angle can be influenced by thetechnology and the designs that are used bydifferent manufacturers. For example, with LEDtechnology there are different designs and patentsrelating to the “bundling” of pixels into the displayelement. One manufacturer has developed a patentfor a lens that encapsulates the LED, causinginternal refraction, thereby increasing the luminanceof each LED pixel as there is less light lost to

dispersion. High luminance at larger viewing anglesenables increased flexibility for installing DMSs inmore challenging environments, e.g., gradechanges. When specifying and testing light-emittingVMSs, it is good practice to ensure that theluminous intensity of a VMS pixel does not decreasemore than 50% when viewed at a specified angle,measured off centre from the optical axis andperpendicular to the display surface (the half-angle).Figure 15 illustrates the viewing angle and itsrelationship to luminance. See Appendix B(References) for documents containing additionalinformation about the test specifications and testingmethodology for optical output of VMSs.

Figure 15 – VMS Viewing Angle and Luminance



Due to the importance of viewing angle to legibility,it is critical that PVMSs be carefully aimed wheninstalled to maximize the viewing time for the driver.


In Ontario, a standard specification for light-emittingVMSs has been developed whereby the luminancedoes not decrease by more than 50% when viewedat a minimum half-angle of 7.5 degrees from theoptical axis and perpendicular to the surface of thedisplay. This has proven to accommodate therequired viewing area in most highway situations.

4.2 Display Characteristics andRequirements

Several key display characteristics, whichsignificantly affect the legibility and hence theeffectiveness of a Dynamic Message Sign, must betaken into consideration when preparingspecifications for the purchase of DMSs. Thesecharacteristics include character and line spacing,fonts, and the use of symbols.

4.2.1 Spacing

Line spacing and character spacing are importantfactors that increase legibility of characters byproviding dark space around each character. Thisblank area ensures that each character stands outon its own and does not blend together withadjacent characters. Typically, spacing is referencedin terms of pixels.

Line spacing should be a minimum of 3 to 4 pixelsand character spacing should be 2 pixels. Spacingbetween words is typically one character width or 9pixels (a 5-pixel character plus a 2-pixel space oneither side). For line-matrix signs the line spacing is

achieved by having no pixels along the permanentstrip between the lines, while for full-matrix signs,the spacing is achieved through rows of unlit pixels.Both methods will meet the required contrast ratios.With more sophisticated sign control capabilities,such as proportional spacing discussed below, somevariation to these guidelines is possible.

4.2.2 Fonts

In situations where the sign technology has thecapability of displaying standard fixed highwaysigning fonts, alphabets, symbols, etc., such asthrough the use of reflective sheeting on rotatingprism CMSs, the fixed signing design guidelinesoutlined in Book 1b (Sign Design Principles) andBook 2 (Sign Design, Fabrication and Patterns) willapply.

In the case of light-emitting matrix signs however,the inherent restrictions imposed by the matrix ofindividual pixels that make up the display present asignificant challenge to achieving good signlegibility. A series of dots simply cannot offer thesame clarity in font design as is available on fixedsigns. Specific design aspects that are relevantinclude:

• character height/width aspect ratio;

• character height/stroke width;

• character spacing;

• borders;

• use of serifs to aid distinction between similarcharacters;

• upper/lower case.

These design parameters are incorporated in variouscombinations to create different font sets.



In general, the higher the pixel resolution on thedisplay, the more closely the font can resemble anideal font design. Higher pixel resolution alsoincreases the complexity and hence the cost of thesign. Some trade-offs must therefore be made in theselection of the most appropriate sign for theintended application.

Based on much research and practical experience,the minimum pixel density necessary to display a fullalphabet of upper case characters for use inhighway applications is a matrix of five pixels wideby seven pixels high (5 x 7). This is a nominalrequirement, as the configuration is actuallydifferent for each character, and is influenced bywhether the display is a continuous matrix ordiscrete characters. Where a full-matrix or line-matrixsign has the capability to accept varied widthcharacters, the font illustrated in Figure 16 andTable 1 should be used. For a discrete charactermatrix VMS or where the control software is unableto accept varied width characters, a fixed 5 x 7matrix font set must be used, although characterssuch as X and W will be compressed. On PVMSs amixture of 4 x 7 matrix font letters and 5 x 7 matrixfont letters, as illustrated in Figure 17, has been usedto allow more text on these narrower signs. Whilethis font is more difficult to read, this is a trade-off toachieve more complete messages.

Lower-case characters require additional rows ofpixels to accommodate the ascenders anddescenders of the characters. The minimumrequirement for lower case character display is anominal 7 x 9 matrix, which adds significantly to thesize and cost of the sign to achieve equivalentlegibility distance. For this reason, it is generallyrecommended that messages on VMSs be displayedin upper case characters only.

Table 1 – Character Spacing forMTO COMPASS Signs



closely as possible the equivalent fixed sign symboldescribed in Book 1. The specific array of pixelspossible will depend on the capability of the sign todisplay graphics characters.

4.3 Sign Dimensions

Overall sign size is a function of the requiredcharacter height and the maximum length of themessage to be displayed. MTO has adopted anapproach wherein overhead gantry-mounted VMSsare capable of 3 lines of text, with 25 characterseach. To ensure that signs are legible at anappropriate distance, the minimum height of theletter on a text sign or the symbol size on a symbolsign must be large enough to accommodate themajority of the driving population.

A considerable body of knowledge has beendeveloped over the years about the requiredmessage legibility and viewing distances fordynamic message signs on highways. The ability ofthe driver to read and understand the message isdependent on character height, number ofcharacters and number of lines, which are in turndependent on operating speeds, minimum requiredvisibility distance, and the messages to be displayed.This section deals with character height. The otheroperating characteristics are addressed in Section 5.

Based on recent human factors research, thelegibility of current LED technology varies with letterheight in a non-proportional fashion. Table 2 showsthe recommended character height for differentmessage characteristics and operating speeds. Forfreeway applications, a minimum character height of450 mm (18 in.) is recommended.

Proportional spacing of characters, in which eachcharacter is spaced at a specific distance from theadjacent character (0, 1 or 2 pixels) appropriate tothe unique shapes of the two characters, enhancesthe legibility of the message. Proportional spacingcan only be achieved when the sign has a line-matrix or full-matrix display and the sign controlsoftware has been developed to specifically takeadvantage of this feature. The character spacingemployed in the MTO COMPASS signs is presentedin Table 1.

MTO has developed font sets which employcharacters of seven pixels in height and from one tonine pixels in width, depending on the character.Each font set is unique to either the permanent VMSor the PVMS and can only be used in line-matrix orfull-matrix signs. These font sets are shown inFigures 16 and 17.

4.2.3 Symbols

The selective use of symbols can increase the levelof understanding of a message; however, cautionshould be exercised in the design and use ofunfamiliar symbols and pictograms, particularlywhen limited by the design parameters of a discretecharacter matrix sign.

Among the most readily recognized and acceptablesymbols in Ontario are arrows and highway number/name identification logos or shields. Certain otherpictograms are in widespread use across Europe,although North American drivers may not be familiarwith their meaning.

Arrows may be used in a passive mode to advise ofexit ramp locations, or in a more active mode inassociation with an advisory message relating tolane changes or full roadway diversions. The designof the arrow on the DMSs should resemble as



Figure 16 – MTO Font for Permanent Variable Message Signs

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c d e k m r t v !

X Y Z

a

P Q R S

T U V W

L M N O

D I J

K

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5 6 7 8 9

A B C

0 1 2 3 4

/ ?



Figure 17 – MTO Font for Portable Variable Message Signs

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Y Z a c k l m

N O P Q R S T U

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7 8 9

A B C D E F

5 540 1 2 3

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4.4 Sign Placement

4.4.1 Freeway Applications

Freeway DMSs are typically placed in advance offreeway-to-freeway interchanges to allow forfreeway-to-freeway diversions resulting fromincidents or scheduled closures. DMSs may also beinstalled prior to major arterials to allow for diversionopportunities. For corridors characterized byrecurring congestion, DMSs may be regularlyspaced along the corridor to provide for queuewarning and congestion management. DMSs shouldbe installed in accordance with the followingplacement criteria:

• DMSs should be located 1,000 m to 1,500 mupstream of freeway interchange decision points;

• DMSs should be located at least 300 mdownstream of visual obstructions includingoverpasses and other signs;

• Overhead DMSs should be located a minimum of300 m upstream of other overhead static signs.

There are three types of mounting that canpotentially be used for freeway applications. Themore common and greatly preferred approach is tomount the DMS overhead, centred over the lanes(See Figure 7). This allows for optimal viewing bythe motorists.

Roadside (ground-mounted or cantilever) DMSdisplays may be considered under one or more ofthe following conditions:

• Rural conditions;

• Two or fewer lanes per direction;

• The intended message content is conducive to asmaller scale display;

• A temporary installation is required.

Depending on the nature of the physical environmentand the roadside mounting configuration, the view ofthe display may be subject to obstruction frompassing heavy vehicles. Figure 8 shows an exampleof a roadside-mounted (cantilever) DMS in NorthernOntario.

DMSs should be installed in accordance with themounting provisions discussed in Section 6.4.

4.4.2 Arterial Applications

DMSs may be located on major arterial roads inadvance of key road network decision points such asfreeway entrance ramps and major intersections.DMSs should be installed in accordance with thefollowing placement criteria:

• DMSs should be located a minumum of 100 mupstream of decision points;

• DMSs should be located at least 100 mdownstream of visual obstructions includingoverpasses and other signs;

• Overhead DMSs should be located a minimum of100 m upstream of other overhead static signs.

DMSs should be installed in accordance with themounting provisions discussed in Section 6.4.

Roadside ground- or cantilever-mounted VMSdisplays may be considered under the conditionsoutlined in Section 4.4.1.

Depending on the nature of the physical environmentand the roadside mounting configuration, the view ofthe display may be subject to obstruction frompassing heavy vehicles.



4.4.3 Queue Warning Signs

Placement guidelines for Queue Warning Signs areas follows:

• Locate upstream of areas with recurringcongestion;

• Locate in areas with higher than average collisionrates;

• Locate upstream of areas with limited sight linedistance;

• Desirable minimum spacing is 300 m anddesirable maximum spacing is 3,000 m betweensigns;

• Locate at least 300 m upstream of static signs;

• Locate at least 200 m downstream of all signsand visual obstructions.

Depending on the nature of the physical environmentand the roadside mounting configuration, the view ofthe display may be subject to obstruction frompassing heavy vehicles.

4.4.4 Lane Control Signs

Placement guidelines for Lane Control Signs are asfollows:

• Locate on roadways operating reversible trafficlanes;

• Locate in areas with specific lane usagedesignation;

• Locate in areas with limited sight line distanceand areas with special safety consideration suchas bridges and tunnels;

• Spacing between signs ranges from 100 m to1,000 m depending on the nature of theapplication, size of display and physicalenvironment. Ideally, a driver should always have atleast two lane-control signs in the lane of travelvisible at all times; and

• Locate downstream of every intersection.

4.4.5 Portable Applications

PVMSs can be installed to support freeway orarterial applications and should be placed inaccordance with the guidelines stipulated inprevious sections of this book. For additionalinformation about the application of PVMSs intemporary situations, reference should be made toOTM Book 7 (Temporary Conditions).

Due to the temporary nature of PVMSs, it is unlikelythat an agency will invest in the capital infrastructureto install an overhead PVMS. Therefore, PVMSs aretypically placed on the side of the road. For semi-permanent locations, the PVMS may be installed onpoles; however, they are typically trailer-mounted.Care must be exercised in order to minimize visualobstructions resulting from barriers, static signs andother structures. The directional sensitivity of light-emitting VMSs, in particular LED-type signs,suggests that great care should be taken in aligningthe optical axes of PVMSs towards the correct pointon the upstream roadway.

The criteria that should be considered when locatinga PVMS include: visibility, roadside safety, andavailability of power and communications.

Visibility

The horizontal and vertical geometry of the highwaywill have the greatest affect on the visibility of thesign. Whenever possible, the sign should be placedon a tangent section of the highway, if it makessense to do so while maintaining the intent of the



message content. The signs shall be installed level.The bottom of the sign display shall be at least1.5 m above the adjacent edge of pavementelevation. The signs shall be set at the proper angleto traffic so that they can be viewed at the highestpossible luminance value. The signs shall be placedso that the messages are legible to approachingmotorists for at least 300 m on freeways and200 m on other highways/arterials. PVMSs shouldnot obstruct, and should not be obstructed by, anyexisting signs or other objects.

Roadside Safety

A PVMS can be a roadside hazard to the travellingpublic. Therefore, when located on highways,PVMSs should be placed outside the clear zone orplaced behind a section of barrier. PVMSs should befar enough behind the barrier to account for thedeflection angle of the given barrier style. Whenchoosing a location for PVMSs, it is important toremember that the sign head is significantly widerthan the trailer when in display position.

For urban applications, PVMSs should be placed soas not to pose a hazard to pedestrians or passingvehicles. Care should also be taken that they do notobstruct the visibility of adjacent signs or the field ofview from intersecting streets.

4.4.6 Site Safety and MaintenanceRequirements

All DMS installations should incorporate appropriatebarrier protection for the mounting structure inaccordance with the requirements set forth in therelevant roadway design safety standards of theimplementing authority.

Field sites should be designed to facilitate safeaccess to the DMS displays and controller cabinetsfor routine maintenance and emergency repairs. Thiswould include consideration of such features as:

• Safe access/egress for maintenance vehicles atthe site;

• Barrier protection for maintenance staff andvehicles on site, including bucket trucks for aerialaccess to the display;

• Walk-in enclosures for overhead signs;

• Integral gantries and safety harness attachmentson the mounting structure to facilitate safe accessto the serviceable DMS components;

• Placing components such as controllers andcabinets at readily accessible ground levellocations.



5. Operational Considerations

Considerations such as message content, alternatedisplay technologies and message comprehensionand credibility are critical to the successful operationof DMSs. In this Section, these operationalconsiderations are discussed as they apply to DMSswith fully variable message content, such as VMSsand PVMSs, as opposed to devices with morelimited displays, such as CMSs.

5.1 Message Content

One of the key activities in the development of VMSmessages is to reach a clear understanding of theoperational objectives of the sign, and to develop anappropriate set of operational strategies. This willgovern the structure and content of the messages tobe displayed.

For greater information about the planning forDynamic Message Signs and other aspects ofAdvanced Traffic Management Systems (ATMS)refer to OTM Book 19 (Advanced TrafficManagement Systems). For signing for TemporaryConditions, refer to OTM Book 7 (TemporaryConditions).

One example of an operating strategy decision iswhether to implement passive or active signing.Passive signing provides factual information relatingto traffic conditions on the road ahead, such as laneblockages, closures or special events, enabling themotorist to make a decision as to whether or not todivert. Active signing, on the other hand, suggestsspecific alternative routes or other specific actions tomotorists. In the case of active signing, cautionshould be used when attempting to direct traffic intoan area where there is little known information aboutcurrent operating conditions. A passive strategy may

be more appropriate. On the other hand, if the roadahead is closed, with no choice but to divert, anactive strategy may be better. Different messagesets can be developed for each condition.

While the choice of passive or active signingdepends in part on the quality and coverage ofinformation collected, this decision is often made ata policy level. Often, such a decision is based onliability considerations and an agency’s perceptionthat they may be at risk by providing activeinformation to motorists, rather than from their lackof ability to provide that level of information tomotorists. A typically sensitive decision is whether todivert traffic from a blocked or congested freeway orexpressway onto a local or regional arterial road, andif so, under what conditions. Indecision ordisagreement between road authorities on suchissues can result in DMSs not being utilized to theirfull potential.

Another aspect of operating strategy is the set ofobjectives for which the DMS messages are to beused by a transportation agency. The first questionthat needs to be asked is what problems are to beaddressed? Once that has been determined, thetransportation agency can develop DMS messagesbased on the identified target audience, the type ofinformation to be conveyed, the degree of driverresponse required, and how the system will beoperated.

Typical DMS objectives applied on a general basisinclude the following:

• Local Incident Management – Identification ofdirectional roadways, streams, ramps, lanes and/or shoulders blocked or closed due to an incident;location (including road name if on a connectingroad, and both upstream and downstream points ifapplicable); and in some cases, information orinstructions on diversion.



• Area-Wide Incident Management –Information on major, severe and lengthy incidents(including weather-related road closures) requiringarea-wide re-routing of traffic through a network;and recommendation of major routes for specificarea-wide target destinations.

• Congestion or Queue Management –Identification of congestion, queues, slow traffic,etc., for recurring and non-recurring congestion;location (including road name if on a connectingroad, and both upstream and downstream points ifapplicable) for drivers upstream of the congestionor queue; and location of downstream point fordrivers within the congestion or queue. To beeffective, congestion and queue managementmessages must be operated in a fully automatedmanner where they can be updated every 20 to60 seconds.

• Express/Collector or Corridor Balancing –Information on relative status of alternate streamsor parallel routes, to enable drivers to make“fastest route” decisions. To be effective, express/collector or corridor balancing messages must beoperated in a fully-automated manner where theycan be updated every 20 to 60 seconds.

• Route Travel Time – Information on currenttravel time(s) to one or two destinations; forlocations with HOV lanes, comparison of traveltimes on the regular route and the HOV route(e.g., number of minutes saved on HOV route). Tobe effective, route travel time messages must beoperated in a fully automated manner where theycan be updated every 20 to 60 seconds.

• Planned Event Management – Information onroad work, special events, etc., similar to thatnoted above for local incident management;advance information on planned event start andend dates and times; information during theplanned event about end date/time; and safespeed for road works displayed during the plannedevent.

• AMBER Alerts – Information provided by policeon child abduction (e.g., description of vehicle)and instructions for drivers (e.g., call 911 ifdescribed vehicle is seen, tune to local media).

• General Warnings – Soft or non-specificmessages advising general driver caution, used forpre-confirmed incident or congestion/queuedetected by automatic means, or for knownincident location where camera viewing isimpeded.

• Default Safety Messages – General safetyreminders for drivers on seat belts, following tooclosely, etc.; seasonal safety warnings, such asattention to school buses, driving in winterconditions, etc.

Once an agency has determined the operationalstrategy and objectives of the DMS, it is importantto find the right structure to the messages, in termsof the length and content, in order to accuratelyconvey the information. There are several factors toconsider when developing the messages. The firstand most important relates to messagecomprehension, and the ability of the motorist tounderstand the amount of information that should bedisplayed on the sign. The amount of informationthat can be displayed is determined by the driver’sexposure time to the message, which is based onthe speed at which the vehicle is travelling and thedistance (therefore the time) over which the sign islegible.

An explanation of the basic principles behind theinterrelationship between sign message length,character height, and the required viewing time/distance may be found in OTM Book 1b (SignDesign Principles) and OTM Book 2 (Sign Design,Fabrication and Patterns). While these fundamentalhuman factors apply to signs in general, recentresearch conducted on signs displaying LEDtechnology has yielded results which applyspecifically to DMSs. (Upchurch et al.) (Ullman et al.)



As discussed in OTM Book 1b and Book 2, goodsign design considers the needs of the majority ofdrivers, rather than the average. A typical target is todesign for 85% of the population, allowing theneeds of 85% of the population to be met. Thisrepresents a reasonable worst case scenario fordesign.

Based on a 1992 study (Upchurch et al.), whichprovided mean, not 15th percentile values, LEDtechnology used in variable message signs has amean legibility of 4.7 m/cm. This means that 4.7 mof legibility distance is available per centimetre ofletter height. The same study indicated a lowermean of 4.1 m/cm for older drivers at night. Basedon a 2005 study (Ullman et al.), current LEDtechnology legibility varies in a non-proportionalfashion with letter height, with 15th percentilelegibility values as follows (see also Table 2):

• 230 mm (9 inch):• day 3 m/cm• night 1.6 m/cm

• 270 mm (10.6 inch):• day 3.6 m/cm• night 2.4 m/cm

• 460 mm (18 inch):• day 5.3 m/cm• night 3.6 m/cm.

Based on the 2005 study, current Ontario freewayoverhead VMSs with 450 mm letters will be legiblefor 239 m (8.5 seconds) during the day, and 162 m(5.8 seconds) at night, based on the 15th percentiledriver. Therefore, a range of 6 to 9 secondsrepresents the typical time that a VMS sign with450 mm high letters is legible for the 15thpercentile driver at a posted speed of 100 km/h.

Other research (Dudek) has suggested that theminimum exposure time of one second per shortword (excluding prepositions or linking words) or twoseconds per unit of information, (e.g., “lane blocked”

or “next exit”), whichever is the largest, should beused to accommodate the needs of unfamiliardrivers. Pictogram reading time is generallycalculated to be one second per symbol.

Other factors that affect exposure time are driverworkload, message familiarity and display format.For driver workload, it is important that the messagebe legible over a long enough distance to allowsufficient exposure time for drivers to attend to thecomplex driving situation and glance at the signoften enough to read and comprehend the message.These factors combine to reduce the effectivemessage exposure time. A maximum of three unitsof information should be displayed at one time, giventhat there is adequate legibility to provide six ormore seconds of exposure time at the operatingspeed. When motorists are given four units ofinformation, one-third of the drivers cannot recall allfour units. Therefore, a maximum of three units ofinformation should be used.

Message familiarity is another factor that affects thereading time for drivers. Message familiarity relatesto the format of the message and what the driver isexpecting to see. Commuters, or other motorists whoare familiar with the network and reading the signs,will recognize message types based on their format.For instance, if information about an incident isbeing displayed, the driver will actually, in a sense,not have to read the word “incident” because theyunderstand the format and can focus primarily onthe location information. This results in the exposuretime required for a frequent road user to read themessage being reduced, in comparison with that ofa road user who is unfamiliar with the system. Aperson who is travelling the network for the first timeor is unfamiliar with the message format will have toread the sign in its entirety, thereby increasing therequired exposure time to the message.

The format of the message is another importantcriterion. Drivers must receive the information in aconsistent manner in order to be able to quicklyunderstand the message, respond to it, and then



have time to implement that response. The formatmust be developed so that drivers can quicklyascertain if a message does not apply to them. Forexample, placing the name of the connectingroadway first in the message immediately targetsonly those drivers who are interested in using theidentified road.

Finally, driver comprehension is a requirement for thesuccess of DMS messages. Testing is required toestablish comprehension. Even when text messagesor pictograms have been in use for many years, theyare not always well understood when tested with thegeneral public. A list of well-understoodabbreviations is available (Dudek et al.). It is alsoimportant to use location terminology that is wellunderstood by the drivers using the roadwaysreferenced in DMS messages, e.g., interchanges,cross-roads, exit numbers, as applicable. If drivers donot understand a message, reading time andincorrect responses increase.

To ensure consistency of application, the ATMSsoftware should provide decision support for creationof messages. In this way, appropriate strategies andmessages which meet the transportation agency’sobjectives and follow the principles of good designcan be developed. This decision support functioncan be applied in two general ways:

(1) Using a static message library, where a list ofmessages pertaining to different situationsand different signs is developed and stored;

(2) Using a rule-based or algorithmic approach,where response rules are defined and appliedto conditions and locations in a structuredmanner, similar to the way in which data areprocessed in an algorithm.

A combination of both approaches is also used.With a static message library, all possible messagesare known and viewable at any time. With a rule-based or algorithmic approach, more testing is

required to ensure the rules behave as expected inall situations. The advantages of this approachinclude flexibility to accommodate a large number ofspecific conditions, consistency, simplicity, accuracy,comprehensiveness, and facility of building plansets. Whichever approach is used, the practice ofoperators creating messages ‘on the fly’ anddispatching them to the signs should be prohibited.

A particular issue for some areas of Ontario is thenecessity to provide bilingual signage. If mandatedfor DMS applications, it would increase thefunctional requirements of the sign. Potentialsolutions include alternating messages (discussedfurther in Section 5.2), increased sign size, andmore signs, while maintaining compliance with themessaging guidelines as defined herein. Additionalsign design considerations pertaining to the displayof bilingual messages on DMSs include thefollowing:

• Consistency in format, so that drivers can quicklyfind the language that they understand, e.g., notmixing multi-phase and single phase formats onbilingual signs;

• Delineation of languages, e.g., showing English onthe upper lines of an electronic or static sign andFrench on the lower lines, separated by ahorizontal line, where practical;

• Limited use of pivot words consisting of an Englishand French term separated by a slash, e.g., to / á,to one per line of text;

• Consistency of pictogram treatment, e.g.,establishing conventions for depicting express andcollector lanes on pictograms, incorporating use ofcolour to convey information, representation of left,centre and right lanes, etc.;

• Grouping of information units together, with oneunit per line of text, if possible;



• Use of pictograms with supporting text (e.g.,similar to the function of educational tab text), andnot using pictograms that provide new informationunsupported by the sign text;

• Simplicity of sign legend and economy of text; and

• Clear communication of the linkage between atraffic event and its location.

In some cases, trade-offs may be required betweendesign considerations. Testing can be used todecide which trade-offs are more effective in termsof driver reading time and comprehension.


Typically, the City of Toronto and the Ministry ofTransportation Ontario utilize passive signing,allowing the motorist to make a decision based onthe information presented on the DMS. The onlyexception is under total closure, where traffic isrequired to exit at a pre-determined location.

A common structure to message development hasbeen implemented within Ontario so that driversreceive information in a consistent manner. Theformat used by the City of Toronto and the Ministryof Transportation Ontario for sign messages is toanswer the following questions in sequence:

• What is the situation being noted?

• Where is the situation occurring?

• What should the driver response be? (activesigning only)

Not all messages will require all of this informationto be displayed to the motorist. The response can beeither explicit, as in the case where a road or lane isclosed at a particular location and so diversion isessential, or implicit, where by providing the location

and nature of the traffic disturbance, drivers canmake their own decisions as to the most appropriateaction to take. The guidelines for information loadingwill also have a bearing on how much informationcan be relayed in a single message.

Both MTO and the City of Toronto use DMSs forlocal incident management, area-wide incidentmanagement, congestion or queue management,express/collector or corridor balancing, plannedevent management, AMBER alerts, and safetydefault messages. In addition, MTO uses DMSs forroute travel time and specific driver impacts ofweather (e.g., high winds on skyway, snowplowingin collector), but not general weather conditions(e.g., drifting snow, fog). The City of Toronto has thecapability of displaying general warnings prior toconfirmation of any incident or queue detected by anautomatic incident or queue detection algorithm.MTO policy prohibits the display of non-traffic-relatedmessages such as advertising, or time andtemperature.

In 2005, MTO conducted a study on how bilingualEnglish and French messages could beaccommodated on VMSs and PVMSs. Approval ofthe implementation plan is still pending. A long listof alternative approaches was evaluated, and humanfactors testing was conducted on the mostpromising alternatives. Preferred alternatives wereselected for implementation. Since they involve theuse of alternative display technologies, they arediscussed in more detail under Section 5.2.

The preferred alternative for accommodatingbilingual VMS messages was the use of existingthree-line VMS installations throughout the FrenchDesignated Area to display bilingual, one-phasemessages. The messages would rely on additionalabbreviations, bilingual words, pictograms andcolour to display existing message content in aconsistent bilingual format, as follows:

• Line 1: English text indicating a condition oraction, e.g., Use Collector Lanes;



• Line 2: Location or unilingual text, e.g., At/ÀKeele Street; and

• Line 3: French text indicating the same conditionor action.

The study also established consistent guidelines fortranslation of original English messages into French.The French translations need to be targeted to anaudience of French-speaking Ontario drivers who,like English drivers, are generally not knowledgeableabout technical traffic terms. The terms used in themessages are similar to current practices usedelsewhere in Canada.

The study showed that PVMS and VMS messagesneed to be adapted to fit under certain spaceconstraints. In certain cases, there is a need toremove articles or interpret, rather than translate, theoriginal English message in a proper linguisticformat. Consistency of language terminology is animportant criterion in message translation.

Other guidelines for French language messagesinclude the following:

• Do not use abbreviations in French signing.Abbreviations are not recognized by French-speaking drivers except for road classificationabbreviations, or days of the week;

• Use the 24-hour clock for French messages.Where applicable, the Ontario format for the 24-hour clock should be used (i.e., 13h30 instead of13:30). Most times shown on messages however,are expected to be on the hour;

• Do not translate terms such as “road”, “avenue”,“drive” or “boulevard”, which are officially part ofplace names established by a municipality orregion, unless the municipality has passed a by-law supporting official bilingual use of these termsin signage as part of the place name (e.g.,Cornwall).

5.2 Alternate Display Techniques

A number of alternate display techniques, usuallyassociated with advertising signs, are technicallypossible in the control of DMSs for highway use.These include:

(1) Message flashing, where the message cycleson and off several times a minute to draw theobserver’s attention to the message. This canoccur with all or part of the message. Flashingmessages take longer to read than staticmessages and should be avoided.

(2) Message alternating, where two physicallyseparate signs, which are close enough to beperceived by drivers as a pair, are used toconvey parts of the message. With theexception of bilingual applications, thisapproach is inconsistent with other types ofsigning on the roadway. It may be confusing todrivers, and should be avoided.

(3) Message scrolling, where the messageappears to scroll from right to left across thescreen or from top to bottom, to accommodatelonger messages than would otherwise bepossible. Message scrolling requiressignificantly more attention from the driver, asdrivers cannot just glance at the message butmust watch it scroll. This constitutes apotentially hazardous distraction and shouldnot be implemented.

(4) Message phasing, where two or more parts ofa message are displayed in sequential timeslots, separated by a brief blank period, toaccommodate longer messages than wouldotherwise be possible. No more than twophases should be used in any application asdrivers have difficulty in remembering morethan two phases. Two unrelated messagesgenerally require more reading time than twoparts of the same message.



(5) Pictogram components, where symbols areused to replace or supplement text displays.Use of colour within pictogram componentscan add further meaning for the motorist, e.g.,use of green for fast speeds, light orange forslow speeds and red for very slow speeds.

In summary, message flashing, alternating orscrolling should be avoided, as these messages aremore difficult and require extra time to read. Thisextra time constitutes a distraction for drivers and istherefore undesirable.

If the sign is not large enough to display the fullmessage required, as is typically the case withPVMSs, and the total message exposure time isadequate, consideration may be given to phasingthe display between two related messages toachieve the desired effect.

If phasing is used, a maximum of two phases isrecommended. The 2005 study of bilingual signingshowed that when three (monolingual) phases wereused, only 55% of younger drivers and 19% of olderdrivers could recall the third phase (see Section 7).Therefore, a design that meets the needs of amajority of drivers should include no more thantwo phases.

Due to the demands of the driving task, a driver maynot be able to read the sign until halfway through aphase. Therefore, the driver should be given morethan one opportunity to read the first phase he/shesees. This means that for a two-phase message, atleast three phases (the first, the second, and arepeat of the first) must be viewed within theavailable legibility window (six to nine seconds forcurrent freeway overhead VMSs at 100 km/h) toallow the driver a second chance to see the firstphase viewed. The FHWA Design Handbook forOlder Drivers and Pedestrians is even more

stringent, recommending that the message shouldbe presented so that it can be read completely,twice – i.e., the opportunity to see four phases for atwo-phase message.

Based on the above considerations, the maximumtime for displaying one message phase on anoverhead VMS is less than three seconds, whichenables the display of no more than three majorwords, or well under two units of information. Giventhat most of MTO’s VMS messages require at leastsix seconds of reading time, the use of messagephasing on overhead (gantry-mounted or roadside)VMSs would not meet human factors requirements,and is not recommended.

PVMSs have more limited message content than theoverhead VMSs, and consequently require lessreading time. Therefore, two-phase messages are aviable option for PVMSs. Each message phaseshould be limited to a maximum of three units ofinformation. Example messages may be found inOTM Book 7 (Temporary Conditions).

The use of alternating messages on separate signsspaced longitudinally along the roadway issometimes proposed as a technique to displaymessages in two languages. While this approach isunwieldy for VMSs due to high capital cost and thedifficulty of placing two VMSs within close proximityto each other, it is a feasible consideration forPVMSs, where message capacity per phase is short,and human factors guidelines limit the number ofphases per message to two. Providing an advanceindication of the language(s) displayed on a givenPVMS (e.g., using colour-coded lettered tabs, and/orcolour-coded tabs) would assist drivers in languagedifferentiation. This type of advance indication wouldreduce the driver requirement to read all signs, andonly require drivers to read those in their preferredlanguage. Because of the requirement to read onlyone PVMS of the pair, the inter-sign spacing couldbe relaxed to as low as 75 m. If multiple PVMSs arelocated close together but showing one language



only, a minimum longitudinal distance of 150 mshould separate the signs because drivers need toread and process the first sign before they see thesecond. The relationship between sign location andlanguage should be consistent from one location toanother (e.g., always put English on the first signand French on the second).

Where part or all of the DMS is available with full-matrix functionality, the potential exists for displayingpictograms containing symbols. Symbols aretypically used alone or in combination withsupporting text on VMSs, or alone as a singlemessage phase on PVMSs. Symbols can conveyseveral words, and are therefore significantly largerand more legible than letters, provided that they arewell-recognized and easily comprehended. Theyoffer an obvious solution for transcending languagebarriers without the additional loading associatedwith two-language text (e.g., more words, impact onlonger reading time, more signs and/or larger signs).They are used internationally, for example in Europe,where many languages are spoken in relatively smallgeographic areas. By installing colour LEDs in thefull-matrix portions of DMSs, the opportunity tofurther enhance symbol meaning and conspicuitythrough colour-coding exists.

Given the current industry standard of PVMSscapable of supporting three lines of text, twoscenarios for PVMS messaging in bilingualdesignated areas are suggested. The first is to use asingle PVMS with two phases, one phase for eachlanguage. The second is to use two PVMSs.


With the exception of pictogram components, theMinistry of Transportation Ontario does not utilizeany of these alternate display functions on thepermanent VMSs, although the functionality has

been incorporated into the signs. Phasing, flashingand alternating displays are used in some cases onPVMSs in work zones. The MTO uses a minimumexposure time of 1.5 seconds per message phase.

According to the 2005 study conducted by theMTO on accommodating bilingual messages onDMSs, the preferred VMS alternative foraccommodating bilingual signing incorporates thedisplay of pictograms on the full-matrix portions ofthe overhead gantry-mounted VMSs (see Figure 6).Information regarding express and collector lanespecific operating conditions is provided in theexisting Central Region Message Library. Tomaintain this level of information using bilingualmessages, the use of pictograms, supplemented bya reduced amount of text, was extensively employedin the study. Further, based on a review of the typicalincident and congestion management messages, itwas determined that many of the express andcollector messages included in the Central RegionMessage Library would be conducive to a pictogramconvention, where the left panel would signify acondition in the express lanes and the right panelwould signify a condition in the collector lanes.

For PVMSs, the preferred bilingual alternative is toaccommodate bilingual messages in one Englishand one French phase, if the message can fit,supplementing with pictograms where applicable. Ifthe message cannot fit into this format, twoalternating PVMSs would be used in longitudinalsuccession. The first PVMS would display twophases in English, and the second two phases inFrench.

The approach using alternating PVMSs has alreadybeen applied by the MTO. Longitudinal spaceconstraints in some locations of Central Region haveprohibited this approach, which requires 150 mlongitudinal spacing between signs. If means suchas colour-coded text or language identification tabsare used to assist drivers in identifying, in advance,



which sign is in the driver’s language of preference,the longitudinal spacing requirement may be relaxedto a minimum of 75 m, depending on the number ofwords in each message phase.

The City of Toronto has implemented messagephasing in order to provide additional information tomotorists. In order to manage the phasing, prioritylevels for the different messages have beendeveloped to ensure consistency in approach. TheVMS located along the Gardiner Expresswayprovides information on both the GardinerExpressway and the parallel arterial, Lake ShoreBoulevard. Level 1 relates to signing for incidents,level 2 for congestion information and level 3 forother advisory signing. These levels are in place forboth the Gardiner Expressway and Lake ShoreBoulevard, with the Gardiner taking precedence. Inthe event of an incident on both roadways, the firstphase of the message would sign for the Gardinerincident and the second phase would sign for theincident on the Lake Shore. The City is of the opinionthat two phase messages are very effective atdisseminating information to motorists. The lowerspeed of the traffic normally present, due toconstruction or routine congestion, typicallycompensates for the additional time required toabsorb the two-phase messages.

5.3 Message Comprehensionand Credibility

Once the transportation agency has implemented aDMS system, it is very important to provide thecorrect information on the signs. The operatingagency must maintain the credibility of the signs.Therefore, agency staff must develop operatingprocedures and standard messages that will be usedconsistently throughout the life of the system. Inorder to ensure that the credibility of the system ismaintained, driver confidence must be achieved andmaintained. Driver expectations must be consideredwhen operating real-time displays. Motorists

travelling along the highway and viewing the DMSswant to see reliable, accurate and up-to-dateinformation. The agency must be willing to supportthe ongoing operation of the system and mustensure that operators are properly trained to provideconsistent responses to incidents. If this is notaccomplished, the messages will lose credibility, asthey may be untimely and inaccurate andconsequently, the drivers will ignore them. Driverswill not react positively to any system that:

• displays information that is contrary to existingconditions, or suggests that existing conditionshave not been detected;

• displays information that is not understood orcannot be read in ample time to make theappropriate manoeuvres;

• recommends a course of action that is notsignificantly better than the motorists’ intendedaction; or

• often tells them something they already know.

In many cases it is much better to display lessinformation, or no information on a sign if theoperator is unsure of the traffic condition.

A subject of considerable debate is the question ofwhat messages, if any, should be displayed on theDMSs when the roadway is operating under normalflow conditions. There are two schools of thought tothis question, both of which have been appliedeffectively around the world.

The first option is to always display a message on asign, regardless of whether or not there is anythingabnormal. The rationale behind this option is that themotorist knows that the sign is working. Duringconditions where the freeway or arterial is operatingin accordance with normal operating conditions,such as during the off-peak period, a safetymessage or a directional signing message can be



put on the display. The disadvantage of thisapproach is that it can reduce the impact value ofhigh-priority messages if drivers becomedesensitized to the VMS messages throughoverexposure to low-priority, default messages.

The second option is to leave the sign blank and todisplay a message only when unusual conditionsoccur. This way, no unnecessary or irrelevantinformation is provided to motorists. It also reducesthe credibility risk of displaying a safety message ordefault directional message at a time whenabnormal congestion or incident information shouldbe displayed, and the problem is evident tomotorists. One of the drawbacks of the secondoption is that this may mean that drivers, when theyapproach a sign that is blank, may not be surewhether or not it is working. It can also lead toquestions from the public concerning the apparentunder-utilization of high-cost infrastructure. Recentevidence from jurisdictions that leave signs blankmost of the time shows that posting a message on anormally blank sign can cause traffic to slow downto read the sign.

At the other extreme is the situation where differentmessages compete for the use of the same DMSdevice and a decision must be made about whichmessage actually gets displayed. These situationsoccur fairly frequently, due to factors such as theoccurrence of secondary incidents, the vulnerabilityof work zones, and the link between incidents andcongestion. Transportation agencies need strategiesfor determining which message has priority underwhich circumstances, particularly since time is at apremium in responding to more than onesimultaneous event. Factors such as severity,proximity, advance knowledge and longitudinalextent are typically used in determining messagepriority. System software that handles this type ofoccurrence in a consistent fashion saves time byexpediting DMS response.

Different types of drivers make up the targetaudience for the DMSs, and it is important to beable to try to reach as many of those drivers aspossible and to provide them with information that isrelevant to their needs. Among the different drivertypes are:

• those who are familiar with the road network, andthose who are not;

• local drivers and visitors;

• business and tourist travellers;

• regular commuters and occasional drivers;

• young and old;

• aggressive and timid;

• urban and rural drivers.

Some of these drivers have similar needs andunderstandings of the transportation network, whileothers may have completely different requirements.One example of this relates to the location namingstrategy utilized on the messages. A local driver orcommuter, familiar with the network, will understandthe sequence of interchanges coming up, and willunderstand destinations that the streets are takingthem to, as well as the location of any upcomingmajor freeway. Other drivers, unfamiliar with thenetwork or travelling through using a map ordirections that they have received, may be lookingfor major freeway-to-freeway interchanges or enddestinations. For this group, information that relatesto a cross-road that they may not be aware of maybe irrelevant to them, as they will not understand theimplications of the message being displayed. Caremust therefore be taken to ensure that the messagestrategy employed will make sense to the majority ofdrivers who will encounter the sign during their



travel. On urban freeways with high levels ofcongestion, commuters usually make up a largepercentage of drivers. Messages are usuallytargeted at commuters for this reason.

It is recommended that operators not be permitted tocreate and display customized messages. A pre-authorized message set should be created inadvance, and operators are responsible forconfirming response messaging proposed by thesystem, as generated using the pre-authorizedmessage set.


Agencies in Ontario that operate Freeway TrafficManagement Systems have traffic managementcentres that are staffed with experienced andknowledgeable staff who are able to use the systemto automatically determine the correct response to avariety of situations, whether it is incidentmanagement, congestion management, safetymessages, scheduled closures or another type ofmessage. Typically the operators are responsible forconfirming the system-generated messaging, andare not provided with the capability to createmessages as part of an event response. Theoperational strategies employed have beendeveloped and have evolved over many years. It isimportant, however, to continually review theeffectiveness of the overall strategies as well as thespecific messages employed, to ensure that theycontinue to serve their intended purposes.

The City of Toronto has incorporated into its VMSresponse software a mechanism for responseconflict arbitration, which automatically suggests apriority message from more than one messagecompeting for any given VMS. The prioritization is inaccordance with City of Toronto policies. The MTO iscurrently developing software which will enableVMS message composition to address simultaneoussituations, e.g., incident together with congestion.

With an increasing number of agencies andcontractors using DMSs, it is important toco-ordinate message content among the variousparties to ensure a consistent, rational approach tomessaging from the perspective of the motorist. TheMTO and the City of Toronto have agreed to displayvariable messages whenever their control rooms arein operation, leaving the signs blank when notattended.

For PVMSs in regions where there is an Operationsor Communications centre, the centre should controlall PVMS messages. This holds true whether it is acontractor-owned sign, an agency-owned sign, or asign rented from a third party.



6. Other Considerations

6.1 Communications

Communication with DMSs can be successfullyaccomplished in a number of ways. Alternativesinclude private communications links or networksover fibre optic cable, over wireless communications,or a combination of the two, or publictelecommunications service providers supplyingaccess to dial-up telephone lines, leased lines, orwireless mobile services. The communicationoptions are listed in descending capital expenditure.DMSs that are installed within or close to an ATMSarea are typically connected to the fibrecommunication backbone or via a wireless linkconnecting to the fibre backbone. DMSs that areinstalled away from the fibre communicationbackbone will usually use dial-up, leased line orwireless services as the capital cost for theinfrastructure is significantly lower. Portableapplications generally use commercial wirelessservices.

Under the ongoing U.S. National TransportationCommunications for ITS Protocol (NTCIP) standardsefforts, standard communications messages (i.e.,objects) have been drafted for various ATMSsubsystems, including DMSs (www.ntcip.org). Thestandard addresses both the transmission rules, andthe format and meaning of standardized messagestransmitted using those rules. The NTCIP DMSstandard is currently under review for updates. Thelatest standard release will include a definition ofobjects governing display of pictograms.

6.2 Power

DMSs should be, as much as possible, installed toutilize utility power not solar power. DMSs typicallyuse 60 Hz, 115 VAC input voltage. Powerconsumption depends on the sign size andmanufacturer, and should be verified prior toarranging the power supply connection. DMSsinstalled within areas with full roadway illuminationshould be designed to utilize existing substationpower. A step-down transformer will be required.DMSs installed in areas with no roadway illuminationshould be connected to a dedicated utility supplypoint of adequate capacity.

Power requirements for portable applications requirespecial consideration, since these signs typically usepower generated by an assembly of solar panels anddeep cycle batteries. The capacity of solar array/batteries should be determined on the basis of signusage. The typical design criteria should assumecontinuous, year-round use of PVMSs at 30% pixelutilization. Designs should give consideration to theefficiency of solar array during short days of fall andearly winter months, as well as the efficiency of thebatteries during cold temperatures, and account forpossible manual recharging of the batteries duringthese periods. For maximum flexibility, the PVMSshould be designed to also use an input voltage of115 VAC, 60 Hz, for locations where utility power iseasily accessible. The sign shall include powersupplies required to convert the input voltage to thevoltage required by the sign components.

When installing a solar-powered DMS, the installershould ensure that the solar panel is directedtowards the south and tilted according to themanufacturer’s recommendation. If this is not done,the power output from the solar array is reduced,which causes premature battery drain.



6.3 Grounding

DMS structures should be installed with appropriategrounding facilities in accordance with local andprovincial codes and regulations.

6.4 Mounting

All assemblies within the sign case should bemounted using shock-, vibration- and weather-resistant hardware in accordance with appropriatelocal and provincial codes and regulations.

When mounted overhead, there should be aminimum vertical clearance of 5.5 m between thelowest point of the DMS/overhead structure and thecrown of the road. For roadside mounting, thebottom of the DMS should be at least 1.5 m abovethe adjacent edge of pavement for visibility reasons.Higher mounting may be required in urban locationsto avoid potential hazards or conflicts withpedestrians.

The display should be mounted perpendicular to thedirection of travel measured at the mid-point of theupstream legibility distance of the sign, confirmedwith a site check prior to final acceptance. It shouldalso have a tilt, typically of 3 degrees from vertical,towards oncoming traffic. Tilting is not a requiredfeature for PVMSs.

6.5 Maintenance Access

Either front access or walk-in maintenance access tooverhead mounted signs is generally acceptable,subject to compatibility with the design of the signsupport structure and the maximum dimensions ofthe sign. The sign design should permit easy accessto the modules, wiring and internal components formaintenance purposes.

Walk-in signs provide a number of advantages. First,maintenance work is conducted inside the sign, andtherefore it does not distract motorists. Workinginside eliminates concerns about weather conditions,provides a safer environment for workers, and alsofor motorists, by eliminating the risk of droppedequipment or materials falling onto the roadway.

If access to the sign is to be gained from a catwalkstructure rather than an enclosure, care must betaken to ensure that the design is such as tominimize the risk of dropping parts, tools, etc., ontothe roadway below. Safety of the workers is ofparamount importance, so elements such as non-skid surfaces, adequate handrails and harness pointsmust be considered.

Consideration should also be given to providing asafe off-road vehicle access site for maintenanceactivities, to minimize the need for lane or shoulderclosures.

6.6 Material Specifications

The structural design for the sign casing, includingthe load on the sign face and mounting hardware,shall comply with the requirements of the currentCanadian Highway Bridge Design Code.

The structural design of the sign and the associatedmounting assembly must be compatible with thedesign of the sign support structure, including anytrusses, columns and foundations. All structuraldesigns (including weight calculations, wind loadsetc.) should be reviewed and attested to by aprofessional engineer licensed to practice in theProvince of Ontario.



The sign case should be constructed of durablematerials. The sign case should provide the requiredprotection and mechanical strength for theapplication. The design must safely accommodatethe maintenance activities required, including easeof opening and closing access panels in an outdoorenvironment.

Sign Face

When the manufacturer’s design calls for theinstallation of weathertight sheeting, (usuallypolycarbonate or “Lexan”) to protect the sign face,the polycarbonate sheets should be uniform fromone panel to another across the sign. Thepolycarbonate sheet system should be designed toallow cleaning of the internal surface of thepolycarbonate sheets.

The sign enclosure and the equipment housed withinshould be protected from moisture, rain, snow, sunradiation, dust, dirt, and salt corrosion found in ahighway environment. The environmental systemshould maintain the internal environment of the signwithin the operating range of all internalcomponents, considering the external conditionsencountered in Ontario. A heating system andthermal insulation should be provided, if required, toprevent any adverse effects on the equipment due tocondensation. A forced ventilation system should beprovided, if required, to mitigate the effects of dustingress and for providing thermal cooling, andthermal equalization. All forced intake air should befiltered.

Control of negative (out-forward) pressure should becarried out as specified by the Canadian HighwayBridge Design Code.

The materials specifications should also address:electronic components, electrical components,cables and wiring, grounding materials and drivingcircuitry.

6.7 Security

Most DMSs have been installed in a freeway orexpressway environment where pedestrian activity isminimal, and therefore vandalism has not been amajor issue. If a DMS is installed in an areaexperiencing pedestrian movement, positive stepsmust be taken in the design to prevent public accessto the sign structure.

Cabinets should have as a minimum a standardtraffic signal lock. Consideration should also begiven to implementing high-security codedcylindrical locks. With this type of lock, the accesscode can be changed after a contractor hascompleted a work assignment. Anti-climb measuresfor the DMS structure legs should also beconsidered.

The hardware and software components should bedesigned to minimize the potential for infiltratingthe system. This has become a greater risk, due tothe use of wireless communication systems, andIP-addressable equipment.



7. AddendumExcerpt from Bilingual Sign Design Study

The Ministry of Transportation Ontario commissioned a Bilingual Sign Design Services report that hasnot been publicly released as of the date of publication of this Ontario Traffic Manual. The BilingualSign Design Services report contains valuable information on human factors considerations, some ofwhich has been included in Section 5 of this manual. To assist transportation practitioners, an excerptof the report is being provided below in its entirety.

Human Factors Design Specifications

This section describes human factors design specifications, which apply to the sign types within thescope of this study. These human factors specifications are used as benchmarks to screen thepreliminary options and later assess in detail the short-listed scenarios.

General

The following guidelines briefly summarize human factors requirements for bilingual variable messagesigns. These requirements are based on studies in which driver visual acuity, reading time, messagecomprehension and message recall have been measured in relation to VMSs. Good design considersthe needs of the majority, rather than simply the “average”. A typical target is to design for 85% of thepopulation. In order to design for a wide range of drivers with respect to literacy and cognitive skills, allrequirements apply to 15th percentile driver performance, and are based on studies involving a widerange of drivers. With respect to legibility, for example, a 15th percentile driver performance of 4 mlegibility/cm of letter height (e.g., a 10 cm character could be read at 40 m distance) would meanthat 85% of the population do better than this, and 15% are worse. Thus the 15th percentile value,which allows the needs of 85% of the population to be met, represents a reasonable worst case fordesign.

Legibility

Based on a 1992 study, which provided mean, not 15th percentile values, LED technology used invariable message signs has a mean legibility of 4.7 m/cm. Therefore, 4.7 m of legibility distance areavailable per centimetre of letter height. The same study indicated a lower mean of 4.1 m/cm forolder drivers at night. Based on a more recent study, current LED technology legibility varies in anon-proportional fashion with letter height, with 15th percentile legibility values as follows:

• 23 cm (9 inch): day 3 m/cm, night 1.6 m/cm;

• 27 cm (10.6 inch): day 3.6 m/cm, night 2.4 m/cm; and

• 46 cm (18 inch): day 5.3 m/cm, night 3.6 m/cm.



Based on the 1992 study, current 400 Series Highway overhead variable message signs with 45 cmletters will be legible for 212 m (7.6 seconds at 100 km/h), based on mean legibility, and 185 m (6.6seconds) based on average legibility for older drivers at night, which is a reasonable worst case.Based on the more recent study, overhead VMS will be legible for 239 m (8.5 seconds) during theday, and 162 m (5.8 seconds) at night, based on the 15th percentile driver.

Therefore, it was determined that six to nine seconds would represent the typical time that a VMS signis legible for the 15th percentile driver at the posted speed of 100 km/h. These values were used toestablish typical exposure times.

Font

A width-to-height (W:H) ratio of 1:1, with single-stroke character width on a 5 x 7 matrix isrecommended to maximize legibility distance. Current VMSs on 400 Series Highways use amaximum W:H ratio of 1:1 (e.g., 7 pixels x 7 pixels for the letters “W” and “X”) to produce 25characters on the 7 x 175 matrix. Increasing the W:H ratio of a PVMS character from 0.7 to 1.0increases legibility by 0.84 m/cm, equivalent to an additional 1.4 sec of reading time at 100 km/hfor 45 cm letter heights. A larger width-to-height ratio reduces the number of characters that can bedisplayed per line, and therefore, per message, on the already constrained capacity of PVMS.

Exposure Time

Current 400 Series Highway overhead VMSs, based on reasonable worst-case legibility, have nineseconds of available reading time (exposure time) during the day and six seconds of available readingtime at night (day), at a driver speed of 100 km/h.

Required time should be tested for specific messages, as the clarity of the message has a majorimpact. In the absence of testing, based on an on-road study to determine 15th percentile readingtimes, approximate assumptions can be made as follows:

• One second per major word (e.g., Accident, Congestion, Lawrence Ave.); or

• Two seconds per unit of information (e.g., at Avenue Rd. or left lane blocked), whichever is longer.

One unit of information answers a question such as “What happened?” “Where did it happen?” “Whateffect did it have on traffic?” “What action should be taken?” “Who should take an action?” etc. Mostcurrent 400 Series Highway overhead VMS require five to eight seconds of exposure time.

Comprehension

Testing is required to establish comprehension. Even when text messages or pictograms have been inuse for many years, they are not always well understood when tested with the general public. A list ofwell-understood abbreviations is available (Dudek, Huchingson, Williams, and Koppa, 1981). If driversdo not understand a message, reading time and incorrect responses increase.



Information Load

A maximum of three units of information should be displayed at one time for a given language, aslong as there is adequate legibility to provide six or more seconds of exposure time at the operatingspeed. When motorists are given four units of information, only about two-thirds can recall all fourunits. Thus a limitation of three units is likely to meet the needs of more than 67% of the population.

Most current overhead VMSs display three units of information. However, several display four or fiveunits of information.

Phasing

A phase refers to a message segment that is individually displayed. For example, the first phase maybe “Construction Ahead” and the second phase “Reduce Speed to 60 km/h.” If phasing is used, amaximum of two phases is recommended. When three (monolingual) phases were used, 55% ofyounger drivers and 19% of older drivers could recall the third phase. Therefore, a design that meetsthe needs of a majority of drivers should include no more than two phases.

Because of the demands of the driving task, a driver may not be able to read the sign until halfwaythrough a phase. Therefore the driver should have more than one opportunity to read the first phase heor she sees. This means that for a two-phase message, at least three messages (the first, the second,and a repeat of the first) must be viewed within the available legibility window (six to nine seconds forcurrent overhead VMSs at 100 km/h) to allow the driver a second chance to see the first phaseviewed. It should be noted that, in recommending an opportunity to read three messages, we areassuming that there is some advantage to the monolingual driver, in that some of the words in onelanguage will be repeated in the other. The FHWA Design Guide for older drivers recommends thatthe message should be presented so that it can be read completely, twice – i.e., the opportunity to seefour phases for a two-phase message.

Based on considerations above, phasing of some of the longer messages in both languages will beproblematic. It is possible to more effectively display information statically than to do so dynamically.

A minimum time of three seconds per phase is recommended, no matter how short the message. Aninter-frame time interval of 0.25 to 0.5 seconds is advisable. Current MTO minimum spacing betweenoverhead signs is 300 m. At 100 km/h this is equivalent to 10 seconds. Even if the current letterheight were to be increased, sign spacing sets a limit of 10 sec of legibility.



Other Design Considerations

In addition to the human factors design specifications, the guidelines for good sign and messagedesign need to be followed. The guidelines for static sign design are described in specific Books of theOntario Traffic Manual (OTM), including Book 1b (Sign Design Principles), Book 2 (Sign Design,Fabrication and Patterns) and Book 7 (Temporary Conditions). The guidelines for VMS and PVMSdesign are covered in OTM Book 10 (Dynamic Message Signs) and Book 19 (Advanced TrafficManagement Systems).

The following sign design considerations pertain in particular to the display of bilingual messages onthe signs within the scope of this study:

• Consistency in format, so that drivers can quickly find the language that they understand, e.g., notmixing multi-phase and single phase formats on bilingual signs;

• Delineation of languages, e.g., showing English on the upper lines of an electronic or static sign andFrench on the lower lines, separated by a horizontal line, where practical;

• Limiting pivot words consisting of an English and French term separated by a slash, e.g., to / á, toone per line of text;

• Consistency of pictogram treatment, e.g., establishing conventions for depicting express andcollector lanes on pictograms, incorporating use of colour to convey information, representation ofleft, centre and right lanes, etc.;

• Keeping information units together, with one unit per line of text, if possible;

• Use of pictograms with supporting text (e.g., similar to the function of educational tab text), and notusing pictograms that provide new information unsupported by the sign text;

• Simplicity of sign legend and economy of text; and

• Ensuring that the linkage between a traffic event and its location is clearly conveyed.

In some cases, trade-off may be required between design considerations. Testing can be used todecide which trade-offs are more effective in terms of driver reading time and comprehension.



Index

AAlternate display techniques, 5.2

Advanced Public Transit System, 2

BBilingual signage, 5.1, 5.2

Blank-out CMS, 3.2

Bulb matrix sign, 3.1

CCandela, 4.1

Changeable Message Sign, 3.2, 3.3, 4.2, 5,Figure 10, Figure 11, Figure 12

Character height, 3.1, 3.3, 4, 4.2, 4.3, 5.1, Table2

Character spacing, 4.2, Table 1

Character width, 4.2

Combination matrix VMS, 3.1, Figure 4, Figure 6,Figure 7

Communications, 6.1

Comprehension, 1.2, 4, 5, 5.1, 5.2, 5.3

Conspicuity, 1.2, 3.3, 4, 4.1, 5.2

Contrast ratio, 4, 4.1, 4.2

Credibility, 3.3, 4, 5, 5.3

DDial-up communication, 6.1

Discrete character matrix VMS, 3.1, Figure 1

DMS placement criteria, 4.4

Driver comprehension, 1.2, 4, 5, 5.1, 5.3

Driver response, 1.2, 4, 5.1

Driver types, 5.3

Driver workload, 5.1

EExposure time, 5.1

FFibre optic cable, 6.1

Fibre optic sign, 3.1, 4.1

Fixed-matrix sign, 3.2

Fluorescent flip-disk sign, 3.1

Fluorescent lamps sign, 3.2

Fold-out/Flap CMS , 3.2

Font, 1.2, 3.1, 4, 4.2, Figure 16, Figure 17

Full-matrix VMS, 3.1, Figure 3

GGantry-mounted, 3.1, 4.3, 4.4, 5.2, Figure 6,

Figure 7

Grounding, 6.3

IInformation load, 1.2, 5.1

Intelligent Transportation Systems, 2

LLane control sign, 2, 3.2, 4.4, Figure 10, Figure 11,

Figure 12

Leased communication line, 6.1

Legibility, 1.2, 4, 4.1, 4.2, 4.3, 6.4

Light-emitting diode, 3.1, 3.3, 4.1, Figure 5

Line matrix VMS, 3.1, 4.2, Figure 2

Line spacing, 4.2

Luminance, 4.1

Luminance ratio, 4.1

MMaintenance access, 6.5

Message comprehension, 1.2, 4, 5, 5.1, 5.2, 5.3

Message content, 1.2, 5, 5.1, 5.2, 5.3

Message credibility, 5.2, 5.3



Message familiarity, 5.1

Message format, 5.1

Minimum vertical clearance, 6.4

Module, 3.1, 3.2, 6.5

Mounting hardware, 6.4

NNTCIP, 1.1, 6.1

PPhoto sensor array, 4.1

Pictogram, 4.2, 5.1, 5.2, 6.1

Pixels, 3.1, 4.1, 4.2

Portable Variable Message Signs, 1.1, 2, 3, 3.3,4.1, 4.4, 5.1, 5.2, 6.1, 6.2, 6.4, Figure 13,Figure 14

Portable variable speed display sign, 3.2

Power supply, 3.3, 6.2

Proportional spacing, 3.1, 4.2

QQueue warning sign, 3.1, 4.4, Figure 9

RResponse (see Driver response)

Road construction (see Work zone)

Roadside-mounted VMS, 3.1, 4.4, Figure 8

Roadside safety, 4.4, Figure 14

Roadway maintenance (see Work zone)

Rotating drum/prism CMS, 3.2

Rural areas, 2

SSecurity, 3.3, 6.7

Serif, 4.2

Sign border, 3.3, 4.1, 4.2, Figure 6

Sign case, 4.4, 6.4, 6.5, 6.6

Sign colour, 1.2, 3.1, 4.1, 5.1, 5.2

Sign enclosure (see Sign case)

Sign face, 1, 3.1, 3.2, 4.1, 6.6

Sign fonts, (see Font)

Sign luminance (see Luminance)

Sign maintenance, 2, 3.1, 4.4, 6.5, 6.6

Sign technologies, 3.1, 3.2, 3.3, Figure 1, Figure 2,Figure 3, Figure 4, Figure 5, Figure 6

Site safety, 4.4, 6.5

Solar panel, 3.3, 6.2

Stroke width, 4.2

Symbols, 4.2, 5.2

TTrailer-mounted DMS, 3.3, 4.4, Figure 13

UUrban areas, 2, 3.3, 4.3, 5.3, 6.4

VVandalism, 3.3, 6.7

Viewing angle, 4.1, Figure 15

Visibility, 3.1, 3.3, 4, 4.1, 4.3, 4.4, 6.4

VMS, 1.1, 3.1, Figure 1, Figure 2, Figure 3,Figure 4, Figure 6, Figure 7, Figure 8, Figure 9,Figure 13

WWalk-in maintenance access, 6.5

Wireless service, 6.1

Work zone, 2, 3.2, 3.3, 5.2, 5.3



Appendix A • Definitions

A

Advanced Public Transit Systems (APTS)The application of advanced electronic andcommunications technologies to improve the safetyand efficiency of public transit systems.

Advanced Traffic Management Systems(ATMS)The application of advanced electronic andcommunications technologies to improve the safetyand efficiency of the road network.

APTSAdvanced Public Transit Systems.

ATMSAdvanced Traffic Management Systems.

B

Blank-out SignA type of CMS with two states, either on or off.When the blank-out sign is off, there is no messagedisplayed. When the sign is on, a pre-determinedmessage is displayed to motorists.

C

CandelaThe basic SI unit of luminous intensity.

CMSChangeable Message Sign.

Changeable Message Sign (CMS)A specific subset of Dynamic Message Signs whichmay display a limited number of fixed messages, anyone of which may be displayed at any given time, ordisplay no message at all. It is an electrical, electro-optical, electro-mechanical, or mechanical signwhich permits the sign message to be changed,either locally or remotely. The messages that can bedisplayed to the motorists are pre-defined. UnlikeVMSs, CMSs cannot be individually configured.

Commercial Vehicle Operations (CVO)The application of advanced electronic andcommunications technologies to improve the safetyand efficiency of commercial vehicle/fleetoperations.

ComprehensionThe ability of drivers to understand the meaning of asign message, including any symbols orabbreviations.

ConspicuityThe ability of a traffic control device to attract orcommand attention, given the visual setting in whichit is placed.

CVOCommercial Vehicle Operations.

D

DMSDynamic Message Sign.

Dynamic Message Sign (DMS)An array of sign technologies that have thecapability of displaying different messages to suitchanging conditions on the roadway. Included withinthe family of Dynamic Message Signs are full-matrixdisplays, single line or character-matrix displays,multiple pre-set message displays and simple on-off



or “blank-out” displays. The terms “Changeable” and“Variable” are used in the OTM to describe specificsub-sets of Dynamic Message Signs.

F

Fibre Optic SignsFibre optic signs are light-emitting signs that utilizea halogen bulb light source and fibre optic cable toilluminate the pixels, which are lenses coupled withshutters that either let the light through or block thelight from being displayed.

I

Intelligent Transportation Systems (ITS)The application of advanced and emergingtechnologies (computers, sensors, control,communications and electronic devices) intransportation to save lives, time, money, energy andthe environment.

ITSIntelligent Transportation Systems.

L

LEDLight Emitting Diode.

LegibilitySign legibility is governed by the distance at whichthe sign becomes legible and the duration for whichit remains legible. Legibility depends on character,word and line spacing, character height, font,contrast ratio and clarity of symbols.

Light-Emitting Diode (LED)Light-emitting diode or LED VMSs are currently thepreferred type of light-emitting sign technology. Thepixels for LED signs are comprised of multiple light-emitting diodes, which are solid state electronicdevices that glow when a voltage is applied.Adjusting the voltage that is transmitted to eachpixel controls the intensity of the light emitted fromeach LED pixel.

LuminanceThe luminous flux in a light ray, emanating from asurface or falling on a surface, in a given direction,per unit of projected area of the surface as viewedfrom that direction, per unit of solid angle.

Luminance RatioThe ratio of the difference in luminance between theON and OFF condition of an illuminated signelement, to the luminance in the OFF condition.

Luminance Ratio = (La – Lb) ÷ Lb

Where:La = The measured luminance (cd/m2) of the

element in the ON-state.Lb = The measured luminance (cd/m2) of the

element in the OFF-state.

M

MatrixA variable message sign display, made up of aseries of dots (pixels) in a matrix format. Parametersor symbols are formed by illuminating differentpatterns of pixels.

ModuleA unit in a character matrix sign, which is comprisedof several pixels and can display an individualcharacter.



N

National Transportation Communicationsfor ITS Protocols (NTCIP)A family of communication protocols developed, orbeing developed, for the transportation community.

NTCIPNational Transportation Communications for ITSProtocols.

P

PixelAn individual dot of light that is the basic unit fromwhich the images on a variable message sign aremade.

Portable Variable Message Sign (PVMS)A Variable Message Sign that may be moved fromplace to place to provide drivers information onconditions, usually work zone conditions, at the timeand place where needed.

PVMSPortable Variable Message Sign.

V

Variable Message Sign (VMS)A specific subset of Dynamic Message Signs. VMSsprovide the highest level of functionality of all of theDMSs. VMSs contain a variable display, made up ofa grid or matrix of discrete dots, known as Pixels.Combinations of pixels render the appearance of acontinuous formed character or graphic symbol. TheVMS can display a full array of alphanumericcharacters and symbols to form messagecombinations and can also have full graphicscapability.

VMSVariable Message Sign.



Appendix B • References

Canadian Highway Bridge Design Code; CAN/CSA-S6-00, CSA International, December 2000

Changeable Message Response Plan DatabaseDevelopment Guidelines; Ministry ofTransportation Ontario, May 1996

Changeable Message Sign Operation andMessaging Handbook; FHWA-OP-03-070, Dudek,C.L., Federal Highway Administration, August2004

Diversionary Content and Behavior; TransportationResearch Record 600, Mast, T.M., Ballas, J.A.,Transportation Research Board, 1976

Electrical Engineering Manual; Volume 4, FreewayTraffic Management Systems (FTMS) ContractDesign, Estimating and Documentation, SpecialProvisions 685S01 – Changeable MessageSigns, Ministry of Transportation Ontario,November 2003

Evaluation of Variable Message Signs: Target Value,Legibility and Viewing Comfort. TransportationResearch Record No. 1376, Upchurch, J.E., Baaj,M.H., Armstrong, J.D., Thomas, G.B.,Transportation Research Board, 1992

Highway Design Handbook for Older Drivers andPedestrians; Report No. FHWA-RD-01-103,Federal Highway Administration, May 2001

Human Factors Requirements for Real-Time MotoristInformation Displays; Volume 1 – Design Guide,Report FHWA-RD-78-5, Dudek, C.L., Huchingson,R. D., et al. Texas Transportation Institute,September 1978

Legibility Distances of Smaller Letters inChangeable Message Signs with Light-EmittingDiodes; Transportation Research Record No.1918, Ullman, B.R., Ullman, G.L., Dudek, C.L.,Ramirez E.A., Transportation Research Board,2005

Manual on Uniform Traffic Control Devices(MUTCD); U.S. Department of Transportation,Federal Highway Administration, 2003

Ontario Highway Bridge Design Code; (ThirdEdition), Ministry of Transportation Ontario, 1992

Ontario Traffic Manual: Book 1 – Introduction to theOntario Traffic Manual; Ministry of TransportationOntario, Publications Ontario, 2001

Ontario Traffic Manual: Book 1b – Sign DesignPrinciples; Ministry of Transportation Ontario,Publications Ontario, 2001

Ontario Traffic Manual: Book 2 – Sign Design,Fabrication and Patterns; Ministry ofTransportation Ontario, Publications Ontario,2005

Ontario Traffic Manual: Book 7 – TemporaryConditions; Ministry of Transportation Ontario,Publications Ontario, 2001

Ontario Traffic Manual: Book 19 – Advanced TrafficManagement Systems; Ministry of TransportationOntario, Publications Ontario, 2007

Optical Performance Functional Specification forDiscontinuous Variable Message Signs;Specification TR 2136 (Issue B), HighwaysAgency U.K., November 1998

Road Vertical Signs – Variable Message TrafficSigns; Part 1: Product Standard, EN 12966-1:2005 prA1, Technical Body: CEN/TC 226,European Committee for Standardization (ComitéEuropéen de Normalisation), 2003

Technology Evaluation for Changeable MessageSigns; Volume 1, Summary Report, Ministry ofTransportation Ontario, 1989

Traffic Control Devices Handbook; U.S. Departmentof Transportation, Federal HighwayAdministration, 1983

Traffic Engineering Handbook; (5th Edition); Instituteof Transportation Engineers, 1999

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