AP-R519-16 Guidance on Median and Centreline Treatments to Reduce Head-On Casualties

7/26/2019 AP-R519-16 Guidance on Median and Centreline Treatments to Reduce Head-On Casualties

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Research Report

AP-519-16

Guidance on Median and Centreline

Treatments to Reduce Head-on Casualties


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Guidance on Median and Centreline Treatments to Reduce Head-on Casualties

Prepared by

David Beck

Publisher

Austroads Ltd.Level 9, 287 Elizabeth StreetSydney NSW 2000 AustraliaPhone: +61 2 8265 3300

[email protected]

Project Manager

Alex Duerden

Abstract

This report presents a compendium of local and overseas practiceand experience in minimising the risk and severity of head-oncrashes. It is intended to assist road safety practitioners identifyeffective actions that can be taken to reduce the incidence andseverity of such crashes, with a focus on median and centrelinetreatments.

In addition to discussing well-proven methods to address head-oncrashes, this report also presents some innovative treatments forwhich there is currently insufficient data to confirm their benefits, butwhich may be effective in reducing head-on crashes where the crash

history does not justify the expense of applying more establishedtreatments.

Abo ut Austro ads

Austroads is the peak organisation of Australasian roadtransport and traffic agencies.

Austroads purpose is to support our member organisations to

deliver an improved Australasian road transport network. Tosucceed in this task, we undertake leading-edge road andtransport research which underpins our input to policydevelopment and published guidance on the design,construction and management of the road network and itsassociated infrastructure.

Austroads provides a collective approach that delivers valuefor money, encourages shared knowledge and drivesconsistency for road users.

Austroads is governed by a Board consisting of seniorexecutive representatives from each of its eleven memberorganisations:

Roads and Maritime Services New South Wales

Roads Corporation Victoria

Department of Transport and Main Roads Queensland

Main Roads Western Australia

Department of Planning, Transport and InfrastructureSouth Australia

Department of State Growth Tasmania

Department of Transport Northern Territory Territory and Municipal Services Directorate, Australian

Capital Territory

Australian Government Department of Infrastructure andRegional

Australian Local Government Association

New Zealand Transport Agency.

Keywords

Head-on crash, centreline treatment, median treatment, road safety

ISBN 978-1-925451-13-9

Austroads Project No. SS1959Austroads Publicat ion No. AP-R519-16

Publication date June 2016

Pages 72

Austroads 2016

This work is copyright. Apart from any use as permitted under theCopyright Act 1968, no part may be reproduced by any processwithout the prior written permission of Austroads.

This report has been prepared for Austroads as part of its work to promote improved Australian and New Zealand transport outcomes byproviding expert technical input on road and road transport issues.

Individual road agencies will determine their response to this report following consideration of their legislative or administrativearrangements, available funding, as well as local circumstances and priorities.

Austroads believes this publication to be correct at the time of printing and does not accept responsibility for any consequences arising fromthe use of information herein. Readers should rely on their own skill and judgement to apply information to particular issues.


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Austroads 2016 | page i

Summary

This report presents a compendium of local and overseas practice and experience in minimising the risk andseverity of head-on crashes. It is intended to assist road safety practitioners identify effective actions that canbe taken to reduce the incidence and severity of such crashes, with a focus on median and centrelinetreatments.

While the body discusses road engineering measures that address the safe roads and speeds pillars of theSafe System framework, some details on methods to address the safe vehicles and road users pillars areincluded inAppendix B.

In addition to discussing well-proven methods to address head-on crashes, this report also presents someinnovative treatments for which there is currently insufficient data to confirm their benefits. Nonetheless,these methods are expected to be effective in reducing head-on crashes, and may be of benefit in situationswhere the site crash history does not justify the expense associated with more established treatments.

Opportunities for further research to confirm benefits of specific treatments have been highlighted.

Appendix A presents an at-a-glance overview of the road engineering based treatments discussed earlier inthis report, including crash modification factors, indicative costs and typical characteristics that may informthe decision to adopt this treatment. Where information has yet to be obtained or is limited, the table alsoidentifies areas of research that could benefit our understanding of road safety solutions.

As with all Austroads guidance documents, this report serves to present an overview of the availabletreatment options only. The reader is advised to consult with the relevant local jurisdiction for the crashmodification factors, costs and treatment lives used for local cost-benefit analysis methods, as well as anyspecific policies or design specifications pertaining to this treatment for that jurisdiction. The reader is alsoadvised to consult with the manufacturer for any product-specific requirements.


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Austroads 2016 | page ii

Contents

1. Introduction ............................................................................................................................................ 1

1.1 Background ...................................................................................................................................... 1

1.2

Key Contributing Factors .................................................................................................................. 1

1.3

Intent of the Report ........................................................................................................................... 2

1.4 Structure of this Report .................................................................................................................... 3

1.5 Crash Modification and Reduction Factors ...................................................................................... 3

1.6

Approved Safety Barrier Products .................................................................................................... 4

2. Centreline Treatments ........................................................................................................................... 5

2.1 Standard Dividing Linemarkings ...................................................................................................... 5

2.2

Raised Profile Centrelines ................................................................................................................ 7

2.3 Raised Profile Centrelines and Edgelines ...................................................................................... 10

2.4

Enhanced Pavement Markings ...................................................................................................... 11

2.5

Raised Reflective Pavement Markers ............................................................................................ 13

2.6 Internally Il luminated Pavement Markers ....................................................................................... 14

3. Median Treatments .............................................................................................................................. 16

3.1 Painted Median .............................................................................................................................. 16

3.2

Pavement Bars ............................................................................................................................... 18

3.3 Wide Centreline Treatment ............................................................................................................ 19

3.4 Raised Median ............................................................................................................................... 22

3.5

Barrier Kerbing on Median ............................................................................................................. 24

3.6 Median Barriers .............................................................................................................................. 25

3.6.1

Rigid Median Barriers ........................................................................................................ 27

3.6.2

Semi-rigid Median Barriers ................................................................................................ 29

3.6.3 Wire Rope Median Safety Barriers .................................................................................... 30

3.6.4 2+1 Roads ......................................................................................................................... 33

3.6.5

Moveable Barriers ............................................................................................................. 35

3.6.6 Motorcyclist Concerns with Median Barriers ..................................................................... 36

3.6.7 Median Barrier Terminal Treatments................................................................................. 37

3.7

Flexible Bollards ............................................................................................................................. 37

3.8 Median Turning Bays ..................................................................................................................... 39

3.9 Median Design ............................................................................................................................... 40

3.9.1 Median Width ..................................................................................................................... 40

3.9.2 Cross-section ..................................................................................................................... 41

3.9.3

Pavement Edge Drop-off ................................................................................................... 41

3.9.4 Median Shoulder ............................................................................................................... 42

3.10Median Glare Treatments............................................................................................................... 44

3.11

Median Plantations ......................................................................................................................... 45

4.

Other Road Infrastructure Solutions ................................................................................................. 47

4.1 Speed Management ....................................................................................................................... 47

4.2 Intermittent Overtaking Lanes ........................................................................................................ 47

4.3

Improved Pavement Surface .......................................................................................................... 49

4.4

Shoulder Treatments ...................................................................................................................... 49


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Austroads 2016 | page iii

4.5

Improved Roadside Forgiveness ................................................................................................... 50

4.6 Curve Delineation and Warning ..................................................................................................... 50

4.7 Addressing Wrong-way Movements .............................................................................................. 52

5. Conclusion ............................................................................................................................................ 55

References ................................................................................................................................................... 56

Summary of Treatments ................................................................................................. 63

Other Countermeasures to Address Head-on Crashes............................................... 68

Tables

Table 2.1: Summary of CRFs and CMFs (bracketed) sourced from various references for raisedprofile centrelines ........................................................................................................................... 9

Table 2.2: Summary of crash reduction and modification (bracketed) factors for application of raisedprofile centrelines and edgelines ................................................................................................. 11

Table 3.1: FSI crash ratio for safety barrier solutions ................................................................................... 27

Table 3.2: Summary of crash reduction and modification (bracketed) factors for WRMB treatmentof head-on, single-vehicle and FSI crashes extracted from selected studies .............................. 32

Table 3.3: Crash modification factors for crashes of varying severity extracted from selected studies ....... 32Table 3.4: Crash modification factors for full-access controlled medians based on width ........................... 40

Table 3.5: Crash modification factors for partial-access controlled or no-access medians basedon width ........................................................................................................................................ 41

Table 3.6: CMFs for varying the median shoulder width on freeways .......................................................... 43

Table 4.1: Summary of various curve delineation treatments and respective crash reduction andmodification factors ...................................................................................................................... 52

Figures

Figure 2.1: Examples of standard dividing linemarkings .................................................................................. 5

Figure 2.2: Close view of raised profile linemarking ......................................................................................... 7Figure 2.3: Example of raised profile centreline ............................................................................................... 8

Figure 2.4: Raised profile centreline and edgeline treatment......................................................................... 10Figure 2.5: Installation of road marking tape .................................................................................................. 12Figure 2.6: Centreline RRPMs during daylight ............................................................................................... 13

Figure 2.7: Centreline RRPMs illuminated at night-time by headlights .......................................................... 13Figure 2.8: Close view of solar-powered centreline IIPM ............................................................................... 14

Figure 2.9: IIPMs illuminating over a long distance ........................................................................................ 15Figure 3.1: Painted median on curve ............................................................................................................. 16Figure 3.2: Painted median on straight section .............................................................................................. 16

Figure 3.3: Typical layout of painted median.................................................................................................. 17

Figure 3.4: Example of pavement bars in median .......................................................................................... 18Figure 3.5: Examples of wide centreline treatments ...................................................................................... 19

Figure 3.6: Layout of painted median outline with raised profile linemarking ................................................ 20Figure 3.7: Wide centrelines highlighted by RRPMs and coloured linemarkings respectively ...................... 20

Figure 3.8: Example of wide centreline designed to allow for overtaking for both flows of trafficand one flow of traffic respectively ............................................................................................... 21

Figure 3.9: Paved raised median ................................................................................................................... 22

Figure 3.10: Grassed raised median providing shelter for signs and lighting .................................................. 22Figure 3.11: Drivers using raised median as transit lane on congested road .................................................. 23

Figure 3.12: Example of median barrier kerbing .............................................................................................. 24Figure 3.13: Further example of median barrier kerbing .................................................................................. 24Figure 3.14: Deflection of errant vehicle by wire rope median barrier ............................................................. 26

Figure 3.16: Linear delineation of concrete barrier on a curve......................................................................... 28


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Austroads 2016 | page iv

Figure 3.17: W-beam barrier along wide median ............................................................................................. 29

Figure 3.18: W-beam barrier along narrow median ......................................................................................... 29Figure 3.19: WRMB in wide centreline ............................................................................................................. 30Figure 3.20: Overlapping of WRMB systems ................................................................................................... 31Figure 3.21: Typical 2+1 road configuration ..................................................................................................... 33Figure 3.22: 2+1 roadway ................................................................................................................................. 34

Figure 3.23: Typical 2+1 road cross-section .................................................................................................... 34Figure 3.24: Images of moveable barrier being transitioned, including over Auckland Harbour Bridge .......... 35

Figure 3.25: Examples of motorcycle barrier post protection systems ............................................................ 37Figure 3.26: Flexible bollards on motorway ...................................................................................................... 38Figure 3.27: Flexible bollards that may later be replaced with WRMB ............................................................ 38

Figure 3.28: Diagram of operation of median turning bays .............................................................................. 39Figure 3.29: Example of median turning bay.................................................................................................... 39Figure 3.30: Examples of uneven pavement edge drop-off ............................................................................. 42Figure 3.31: Example of paved median shoulder on highway ......................................................................... 43Figure 3.32: Antiglare screens ......................................................................................................................... 44Figure 3.33: Median plantation ......................................................................................................................... 45

Figure 4.1: Roadway featuring intermittent overtaking lanes ......................................................................... 48

Figure 4.2: Delineation of curve with CAMs ................................................................................................... 51Figure 4.3: Delineation and warning of curve with vehicle activated signage and chevron board................. 51

Figure 4.4: Drive on left in Australia signage used in the Barossa Valley.................................................... 53Figure 4.5: Wrong way/go back signage at motorway exit (inset shows greater detail) ................................ 54


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Austroads 2016 | page 1

1. Introduction

1.1 Background

The Safe System approach to road safety has been adopted in Australia and New Zealand. This approachaims to provide a road system that protects compliant road users from death and serious injury. A SafeSystem approach also recognises that road users are fallible and will continue to make mistakes, but thatthey should not be penalised with death or serious injury when they do. Part 1 of the Austroads Guide toroad safety(Austroads 2013) discusses the Safe System approach in detail.

In part, the Safe System approach requires (Australian Transport Council 2011):

Designing, constructing, and maintaining a road system (roads, vehicles and operating requirements) sothat forces on the human body generated in crashes are generally less than those resulting in fatal ordebilitating injury.

Improving roads and roadsides to reduce the risk of crashes and minimise harm. Measures for higherspeed roads include:

segregating traffic

providing and maintaining forgiving roadsides

providing clear driver guidance.

Managing speeds, taking into account the risks on different parts of the road system. In areas with largenumbers of vulnerable road users or substantial collision risk, speed management supplemented by roadand roadside treatments is a key strategy for limiting crashes.

The term head-on crash refers to an event in which a vehicle departs from its laneway into opposing traffic,such that any portion of the leading edge of its vehicle strikes any portion of the leading edge of an opposing

vehicle. This is one of the most severe crash types that may occur. It is therefore important within a SafeSystem that practitioners are aware of measures available to reduce the incidence and severity of this crashtype.

In an average year, there are about 74 fatal head-on crashes in urban environments and 264 in ruralenvironments in Australia and New Zealand combined (Austroads 2014a; Austroads 2010a).

Head-on crashes in rural areas are generally high-speed crashes that result in serious injury outcomes.Whilst new vehicles are designed and tested to ensure head-on collisions are survivable at speeds of up to70 km/h, in real life scenarios, the combined relative speeds in a rural crash can exceed 200 km/h. Ininteractions between light and heavy vehicles, much of the impact energy from this relative speed will betransferred to the light vehicle. The high severity of this crash type is demonstrated by their high fatality rate

19% of head-on crashes occurring on rural roads in Australia and New Zealand result in a fatality

(Austroads 2010a).

1.2 Key Contributing Factors

A high proportion of head-on crashes occurs on or near curves, when a vehicle crosses the centreline of theroad to collide with an oncoming vehicle or object located on the edge of the carriageway. This is an issueparticularly when the operating speed is higher than the design speed for a curve, requiring drivers to reducetheir speed. Complex curves, featuring more than one curve in close proximity, are also overrepresented athead-on crash sites. Centreline encroachments on left curves are generally a result of excessive speeds oravoidance of roadside hazards, whilst on right curves encroachments are generally due to drivers cutting thecorner or straightening on the curve if they consider it safe to do so (Austroads 2010a; Austroads 2014a).

A high proportion of head-on crashes on rural roads occur in wet conditions (19% in Australia and 29% inNew Zealand).


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On rural roads, the following road design characteristics have been identified as common features of siteswith high head-on crash rates (Austroads 2010a):

poor sight distance for overtaking due to horizontal and vertical curves

unsealed or partially sealed shoulders

inappropriate speed limits

poor curve delineation insufficient or unclear advisory/warning signs, such as for curves, advisory speeds, intersections, etc.

insufficient or poorly maintained raised reflective pavements markers (RRPMs) delineating the road andvehicle lanes.

On urban roads, the following road design characteristics have been identified as common features of siteswith high head-on crash rates (Austroads 2014a):

steep downhill gradients leading into curves

limited sight distance both at intersections (signalised and unsignalised) and mid-block

presence of visually imposing or unforgiving roadside furniture that may encourage drivers to travelfurther from the road edge, reducing the buffer from opposing traffic.

Poor coordination of horizontal and vertical alignments are also a key contributing factor to vehicle loss-of-control, which can result in head-on crashes (Austroads 2015a).

Heavy vehicles are involved in a notable proportion of rural head-on crashes (17% in Australia and 10% inNew Zealand). Head-on crashes are the second most common crash type for heavy vehicles on rural roadsin Australia, and the most common crash type for heavy vehicles on rural roads in New Zealand (Austroads2009c). These crashes result in more severe outcomes, with 28% of such crashes on rural roads resulting ina fatality, compared to 19% for all rural head-on crashes (Austroads 2010a).

1.3 Intent of the Report

This report presents a compendium of local and overseas practice and experience in minimising the risk andseverity of head-on crashes. It is intended to provide guidance to practitioners on effective actions that canbe taken to reduce the incidence and severity of head-on crashes, with a focus on road engineeringmeasures, particularly median and centreline treatments.

Median and centreline treatments are generally effective by providing:

a visual separation of vehicles (e.g. centreline markings)

a kinetic deterrent to vehicles crossing the median (e.g. raised profile linemarkings)

a physical deterrent to discourage vehicles from crossing the median (e.g. raised median)

a physical obstruction to prevent vehicles crossing the median (e.g. median barriers).

Some of the treatments discussed will also assist in reducing other crash types, and so application of thesetreatments can have additional benefits to their ability to address head-on crashes. Alternately, sometreatments, whilst addressing head-on crashes, may create other unintended road safety issues. Thepractitioner is advised to carefully consider what implications, whether positive or negative, a particulartreatment may have.

The reader is advised to consult with the relevant local jurisdiction for specific details relating to a treatment,such as crash modification factors, costs and treatment lives used for local cost-benefit analysis methods, aswell as any specific policies or design specifications pertaining to this treatment for that jurisdiction. Thereader is also advised to consult with the supplier for any product-specific requirements.


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1.4 Structure of this Report

The report is comprised of six sections, as follows:

Section1 (this section) presents the background to the Austroads project and outlines the scope andintent of the report.

Section2 presents local and international experience in using centreline treatments to address theincidence and severity of head-on crashes.

Section3 presents local and international experience in using median treatments to address theincidence and severity of head-on crashes.

Section4 discusses other road engineering based countermeasures to address head-on crashes,included speed-based treatments.

Section5 provides the concluding comments, including the key findings and limitations of the research,as well as identification of areas for future study in the area of treating head-on crashes.

An at-a-glance overview of all centreline, median and other road engineering based countermeasures isincluded inAppendix A.

This section also includes indicative costs for treatments. As can be seen, many of these costs varysignificantly between jurisdictions. Costs are a guide only to assist in comparing treatments. Practitioners areadvised to consult with their local jurisdiction for more accurate cost estimates when preparing a cost-benefitanalysis. Costs may vary based on the jurisdiction, project scope, site location and other environmentalfactors.

Having considered road and speed-based treatments in the report,Appendix B has been included toconsider the other pillars of the Safe System, namely vehicle and behavioural based countermeasures.Whilst these are not road-based treatments, and therefore not included in the main body of the report, it isimportant for road safety practitioners to be aware of other solutions available within the Safe System.

1.5 Crash Modification and Reduction Factors

In discussing treatments, this report aims to identify the respective crash modification and reduction factors.According to the Austroads Glossary of Terms(Austroads 2015b):

The crash modification factor (CMF) is a representation of the relative change in crash frequency thatoccurs due to a specific change in the road or its immediate environments.

The crash reduction factor (CRF) is an indication of the expected percentage reduction in road crashesfollowing the introduction of a countermeasure.

To illustrate, a CRF of 60% would suggest that 40% of crashes would remain. The CMF would therefore berepresented as 0.4. A treatment with a negligible CRF would have a CMF of 1.0, indicating that the samecrash rate would remain after application of the treatment. A negative CRF of20% indicates a 20%increase in crashes, so would be indicated as a CMF of 1.2.

CRFs and CMFs are general indications only, and may vary due to a range of factors. All values presented inthis report have been rounded to the nearest 5%. Presenting factors with greater accuracy would potentiallymislead the reader as to the accuracy of the research and its applicability to individual scenarios. Thesevalues have been presented as a guide only, and practitioners should consult their local jurisdictions forpertinent CMF values when preparing cost-benefit analyses.

Section 4.6 of the Austroads Guide to road safety (Austroads 2015c) provides guidance on how to determinethe CRFs for applying multiple treatments at one site.

Most research reviewed for this project reported only the crash reductions for all crash types combined, anddid not consider reductions for head-on crashes explicitly. Where crash reductions are for head-on crashesin particular, this has been indicated.


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1.6 Approved Safety Barrier Products

Safety barrier products referenced in this publication are included as examples of treatments used indifferent road environments and countries. Contact your local road agency for products approved for use inyour jurisdiction.


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2. Centreline Treatments

2.1 Standard Dividing Linemarkings

Delineation is designed to visually guide drivers safely along the roadway by influencing their choice ofposition and speed. When delineation is lacking or inadequate, the driving task becomes more difficult, anddrivers have a greater chance of leaving their travel lane. If the lane departure is to the right, the nominalcentreline of the road is crossed and a head-on crash may occur. Drivers may also decide to conduct anovertaking manoeuvre (either permissible or illegal), which on two-lane roads will require all or part of thevehicle crossing into the opposing lane.

The Australian Standard, AS 1742.2-2009 covers the design of centreline markings (referred to as dividinglines) for use in Australia1. The markings may comprise a:

1. double two-way line, consisting of two continuous lines side by side, indicating that crossing of the line is

prohibited for both travel directions

2. double one-way barrier line, featuring a continuous line beside a broken line, indicating that crossing ofthe line is permitted only for traffic travelling on the left of the broken line

3. single barrier line, featuring a single continuous line, indicating that no overtaking is permitted, butcrossing by traffic entering or leaving the roadway is permitted

4. dividing line, featuring a single broken line, serving to separate traffic, but allowing crossing of the line fortraffic travelling in either direction.

Figure 2.1 shows examples of each dividing linemarking.

These linemarkings and the associated rules are referenced in theAustralian Road Rulesand the New

Zealand Road Code. Legislation in all jurisdictions in the two countries requires compliance with these rules,which are enforceable by the police and which may have a bearing on the outcome of civil actions. In manyjurisdictions, emerging road regulations allow vehicles to cross the centreline, where it is safe to do so, toenable a minimum 1 metre passing distance (clearance) to cyclists. The safety impact of this recentdevelopment will need to be monitored over time.

Dividing lines are not generally used on sealed roads of less than 5.5 m width, given that in practice thedrivers of most cars and larger vehicles would have no choice but to straddle the centreline.

Figure 2.1: Examples of standard dividing linemarkings

(a) Double two-way line (b) Double one-way barrier line

1Each jurisdiction is likely to provide their own policy on how to apply AS 1742.2-2009 locally.


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(c) Single barrier line (d) Dividing line

Source: ARRB Group.

When the traffic volume is very low, e.g. under 300 vehicles per day (vpd) on rural roads, and under 2500vpd on urban roads, dividing lines may be omitted. Dividing lines are also recommended for use under thefollowing conditions (AS 1742.2-2009):

frequent horizontal or vertical curves

substandard curves

areas subject to fog

minor road approaches to intersections with STOP or Give Way signs

curves or crests in residential streets

where crash records suggest a need

to help ensure continuity of an arterial road

where there are significant volumes of night-time or tourist traffic.

Lines used within the central third of the road are generally preferred to be 100 mm wide, though may be as

narrow as 80 mm (AS 1742.2-2009). The wider the linemarkings, and the greater the distance betweendouble linemarkings (known as the separation), the greater the separation between vehicles. Doublelinemarkings with wide separations can be used as a distinct treatment, known as the wide centrelinetreatment, discussed in Section3.3 (Austroads 2010e).

Crash modification

The New South Wales Roads and Maritime Services (Roads and Maritime) (2015b) suggests a 15%reduction in head-on crashes (CMF of 0.85) for the installation of barrier lines (i.e. both providing delineationand barring overtaking).

Austroads (2010d) indicates that centrelines can reduce total crashes on a road by 30% (CMF of 0.70). By

preventing overtaking as well as, barrier lines and double two-way lines have a higher crash reduction of35% (CMF of 0.65).

Treatment life

Austroads (2010f) suggests a treatment life of three years can be applied for standard linemarking systems.However, the precise rate of wear at a location is unknown and can be accelerated at certain locations bytraffic, roadside activities, weather and other factors.


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2.2 Raised Profile Centrelines

Raised profile centrelines (also known as audible centrelines, audio-tactile centrelines or centreline rumblestrips) are raised or grooved patterns placed on or near the roadway centreline. Other audible centrelinescan be achieved using grooved patterns on or near the centreline.Figure 2.2 shows a close-up view of theraised profile linemarking, whilstFigure 2.3 shows raised profile linemarking located along a centreline.

Such features alert drivers when their wheels reach the centreline by emitting a humming sound andvibrations that are clearly distinguishable from the normal driving experience. As they alert drivers when theirvehicle strays towards opposing traffic, raised profile centrelines are most effective at addressing crashesrelated to driver inattention, distraction or drowsiness (Bahar, Wales & Longtin-Nobel 2001).

Figure 2.2: Close view of raised profile linemarking

Source: AllState LineMarking Australia (n.d.).

As well as providing a clearly audible signal, centreline rumble strips improve visibility of the centreline(especially in wet conditions) and discourage drivers illegally crossing the centreline, such as for overtaking

(Torbic et al. 2009; Neuman et al. 2003).Raised profile centrelines may be installed without any changes to the roadway cross-section, therebyserving as a relatively fast and low-cost measure (Neuman et al. 2003). They have been found to betraversable by motorcyclists without causing loss-of-stability (Jamieson et al. 2013).

The literature reviewed has determined potential operational issues with raised profile centrelines. Theimplications of these concerns will need to be considered on a case-by-case basis:

additional maintenance requirements (Neuman et al. 2003)

high noise levels (Neuman et al. 2003)

potential for water ponding if not adequately drained (Bahar, Wales & Longtin-Nobel 2001)

potential for presenting a visual obstruction to overtaking manoeuvres (Neuman et al. 2003).


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Figure 2.3: Example of raised prof ile centreline

Source: ARRB Group.

Practitioners are advised to consider cyclist movements when installing raised profile centrelines since the

treatment may encourage drivers to travel closer to the shoulder, reducing the lateral distance betweenvehicles and any cyclists travelling on or close to the shoulder (Neuman et al. 2003; Kar & Weeks 2009).

To mitigate the noise levels associated with this treatment, whilst still ensuring an appropriate audible signalto the driver, Torbic et al. (2009) recommend a lower sound level in built-up areas, of612 dBA in the occupant compartment, compared to 1015 dBA away from residential areas. Noise levelsvary depending on the design of the rumble strips. Practitioners should check with the manufacturer toconfirm that noise levels are appropriate for the particular road design.

Crash modification

Table 2.1 summarises a number of CRFs and CMFs for the installation of raised profile centrelines, sourced

from various references. As can be seen, this treatment type both reduces the incidence and severity ofhead-on crashes. It is suggested that the severity of head-on crashes is reduced as drivers are alerted toundertake a degree of emergency braking and/or steering with the effect of reducing the impact speed andthe extent of the impact area.

In addition to the information provided inTable 2.1,Hirasawa et al. (2006) found that raised profilecentrelines reduced head-on crashes by 55%, fatalities by 70%, serious injuries by 30% and minor injuriesby 25% (CMFs of 0.45, 0.30, 0.70 and 0.75 respectively). These results indicate a greater success atreducing fatal crashes compared to reducing FSI crashes as presented inTable 2.1.


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Table 2.1: Summary of CRFs and CMFs (bracketed) sourced from various references for raised prof ile

centrelines

Environment Head-on (all) FSI(1)head-on All crashes All FSI crashes

Range from allstudies below

2055%

(0.450.80)2565%

(0.350.75)915%

(0.850..91)1030%

(0.700.90)

Austroads(2010d)

15% (0.85)

Sayed, deLeurand Pump (2010)

30% (0.70)

Kar and Weeks(2009)

25% (0.75) 50% (0.50) 30% (0.70)

Torbic et al.(2009)

Urban two-lane 40% (0.60) 65% (0.35)

Torbic et al.(2009)

Rural two-lane 30% (0.70) 45% (0.55) 10% (0.90) 10% (0.90)

Hirasawa et al.(2006) 55% (0.45)

Harkey et al.(2008)

Rural two-lane 20% (0.80) 25% (0.75) 15% (0.85) 15% (0.85)

Persaud, Rettingand Lyon (2004)

25% (0.75) 10% (0.90) 15% (0.85)

1 Fatal and serious injury.

Note: Crash reduction for FSI crashes is an important focus for the Safe System approach.

Where raised profile centrelines are installed on a road already featuring raised profile edgelines, the head-on crash reduction benefits are even greater. Olson, Sujka and Manchas (2013) reported the following crash

reductions: Crossover/head-on crashes

65% reduction in head-on crashes (CMF of 0.35)

25% reduction in FSI head-on crashes (CMF of 0.75)

Other crash types

10% reduction in overall crashes (CMF of 0.90)

25% reduction in FSI crashes (CMF of 0.75)

10% increase in run-off-road to the left crashes (CMF of 1.10)

negligible impact on FSI run-off-road to the left crashes (CMF of 1.00).

See the following Section2.3 for further details on the performance of raised profile centrelines withedgelines.

Treatment life

Austroads (2010f) suggests a treatment life of five years for raised profile centrelines.


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2.3 Raised Profile Centrelines and Edgelines

Olson, Sujka and Manchas (2013) reports that installing raised profile centrelines in concert with raisedprofile edgelines (Figure 2.4)was a particularly effective, low-cost method to address lane-departure (i.e.head-on and run-off-road) crashes on two-lane rural roads.

Figure 2.4: Raised prof ile centreline and edgeline treatment

Source: Transport for NSW (TfNSW), private communication, January 2015.

Crash modification

Whilst Olson, Sujka and Manchas et al. (2013) report that raised profile edgelines led to a slight increase inthe rate of head-on crashes, when installed with raised profile centrelines, both run-off-road and head-oncrashes were reduced.

Table 2.2 summarises a number of crash reduction and modification factors for the installation of raised

profile centrelines and edgelines together, sourced from various references. As can be seen, this treatmenttype reduces both the incidence and severity of head-on crashes. It is suggested that the severity of head-oncrashes is reduced as drivers are alerted to undertake a degree of emergency braking and/or steering inputwith the effect of reducing the ultimate impact speed.

Lyon, Persaud and Eccles (2015) note that the results obtained in the study were conservative as not allsites used in the study were ideal candidates for this treatment and therefore the benefits were less notable.Generally, it would be expected that this treatment should yield even greater crash reductions than thosepresented in the study.

Treatment life

As with raised profile centrelines, raised profile centrelines and edgelines together have a recommendedtreatment life of five years (Austroads 2010f).


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Table 2.2: Summary of crash reduction and modification (bracketed) factors for application of raised profile

centrelines and edgelines

Head-on (all)FSI head-

on (1)All crashes

Lane-departure

(all)(2)

FSI lane-

departure

Range from all

studies below

3565% (0.350.65) 30% (0.70) 20% (0.80) 2065% (0.350.80) 45% (0.55)

Lyon, Persaudand Eccles (2015)

35% (0.65) 20% (0.80) 25% (0.75)

Olson, Sujka andManchas (2013)

65% (0.35) 30% (0.70) 65% (0.35) 45% (0.55)

Sayed, deLeurand Pump (2010)

20% (0.80)

1 Crash reduction for FSI crashes is an important focus for the Safe System approach.2 Head-on crashes are a subset of lane-departure crashes and therefore included in this list.

2.4 Enhanced Pavement Markings

Enhanced pavement markings, also termed long life road markers, improve the reflectivity of road markers toimprove their night time visibility. Smadi et al. (2010) demonstrate that increasing the retroreflectivity ofcentrelines helps to reduce the crash rate on roads during times of darkness. Head-on crashes and singlevehicle crashes are identified as the target crash types affected by this treatment.

However, Harwood et al. (2014) suggest that improved visibility of delineation is only effective on roads withgood horizontal and vertical alignment. When applied on poorer quality roads, it can encourage higherspeeds inappropriate for the environment and result in a general increase in crashes (Harwood et al. 2014).

It has been suggested that improvements to the centreline marking visibility will be most effective when

edgeline markings are similarly improved (Avelar & Carlson 2014).

Profiled thermoplastic centreline stripes

Profiled thermoplastic centreline stripes are considered a moderate cost treatment that improves the visibilityof a centreline system at night-time, particularly in wet conditions (Neuman et al. 2003). As it is a moderatecost, durable treatment, it is widely used (Bahar et al. 2006).

Another advantageous feature appears to be that these features provide a mild audio-tactile response,alerting drivers straying from their lanes. However, the audio-tactile response is less noticeable for largervehicles, especially trucks (Neuman et al. 2003).

According to Neuman et al. (2003), this treatment suits road sections meeting the following conditions:

sections with relatively long unbroken centrelines

traffic volumes and head-on crash history do not justify raised profile centrelines or other more expensivetreatments

wet-weather crashes are high

resurfacing or other pavement maintenance is not scheduled for at least three years.

Cold applied plastic materials

Cold applied plastic material is a two-part liquid mix of a resin-based material and a hardener. To improve

reflectivity, glass beads are pre-mixed into the product, and additional beads are dropped on duringapplication. Due to its high wear resistance, this treatment is generally used for marking intersections(VicRoads 2014).


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Road marking tape

Road marking tapes have a high initial cost compared to other linemarking options, so that their use isgenerally restricted to limited areas where a high level of performance is required under severe conditions, orto minor treatments to repair or replace sections of deteriorated linemarking. Tape may be produced flat orprofiled and retroreflective glass beads are incorporated into the material during its production.

Tape retroreflectivity is about four to six times that of waterborne traffic paints. However, their retroreflectivityquickly diminishes, with a useful life span of three years (Bahar et al. 2006).

Figure 2.5 shows the installation of road marking tape for treating a short section.

Figure 2.5: Installation of road marking tape

Source: Main Roads Western Australia (MRWA), private communication, September 2015.

Crash modification

Enhanced pavement markings can reduce night-time mid-block crashes by 10% (CMF of 0.90) (Migletz &Graham 2002). When isolating high crash frequency sites only, it is suggested that this treatment can reducecrashes by 15% (CMF of 0.85). Whilst these CRFs do not differentiate by crash type, it is generally acceptedthat this treatment has the greatest impact on run-off-road and head-on crashes (Donnell, Karwa &Sathyanarayanan 2009).

Treatment life

Austroads (2010f) suggests a treatment life of five years for thermoplastic markings. For retroreflective tape,Bahar et al. (2006) indicate a useful treatment life of three years.


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2.5 Raised Reflective Pavement Markers

RRPMs, also sometimes known as retroreflective pavement markers, cats eyes or road studs, are used toaugment the visibility of road markings. As the name suggests, the markers are raised, yet of trafficableprofile, and are reflective such that they are illuminated by approaching vehicle headlights (AS 1742.2-2009).

Figure 2.6 shows centreline RRPMs during daylight, whilstFigure 2.7 shows centreline RRPMs illuminatedby headlights at night-time.

Figure 2.6: Centreline RRPMs during daylight

Source: ARRB Group.

Figure 2.7: Centreline RRPMs illuminated at nigh t-time by headlights

Source: MRWA, private communication, September 2015.

RRPMs are conspicuous under a range of conditions, including wet night-time conditions. Additionally, theyprovide an audio-tactile signal when traversed by vehicle wheels, adding another stimulus to alert errant

drivers (AS 1742.2-2009).


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Centreline RRPMs may be placed 2550 mm from either side of dividing lines. Centreline RRPMs should beyellow to differentiate them from edgelines RRPMs (red) or lane line RRPMs (white) (AS 1742.2-2009).

Crash modification

Austroads (2010d) suggests that installation of RRPMs should reduce all types of crashes at a site by 5%

(CMF of 0.95) for all crashes.

It is suggested that this treatment may reduce all types of dry night-time crashes by 10% (CMF of 0.9), andall types of wet night-time crashes by 20% (CMF of 0.8) (Ermer et al. 1991 in Austroads 2010e).

Gan, Shen and Rodriguez (2005) indicate a head-on crash reduction of 15% (CMF of 0.85) for thistreatment.

Treatment life

Austroads (2010f) suggests a treatment life of five years for RRPMs. However, the effective life of RRPMsdepends critically on the precise location where they are installed. While a five-year life may be possible foran RRPM installed on the outside of an edgeline on a low-volume road, a much shorter life would beanticipated for an RRPM on a centreline that is frequently crossed by vehicles.

2.6 Internally Illuminated Pavement Markers

Internally illuminated pavement markers (IIPMs), also known as LED raised pavement markers or intelligentroad studs, are a similar concept to RRPMs, but are self-illuminating. This serves to provide enhanceddelineation, or delineation when RRPMs are not considered fully effective. Power may be provided via solarpanels on the IIPMs, or through underground wiring (VicRoads 2005).Figure 2.8 shows a close view of asolar-powered centreline IIPM.

Figure 2.8: Close view of solar-powered centreline IIPM


It is opined that IIPM centrelines may be considered more effective than RRPMs on curves, crests orfreeway ramps where the road alignment does not allow vehicle headlights to adequately illuminate RRPMs(VicRoads 2005).

Otherwise, IIPMs may be preferable when it is important to provide delineation over longer distances thanvehicle headlights may illuminate (Figure 2.9). IIPMs can provide illumination over 900 m, as compared toRRPMs, which can typically provide illumination from headlights over 90 m (Highway Engineering inAustralia 2008).


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Figure 2.9: IIPMs illuminating over a long distance


Centreline IIPMs should still be retroreflective so they can provide some illumination even if the power sourceor internal electronics or lighting systems fail. They should retain the same colouring format as for RRPMs(i.e. yellow along centrelines) (AS 1742.2-2009; VicRoads 2005).

IIPMs are still an emerging technology, and some makes are more reliable than others. Practitioners shouldconsult with their local jurisdiction for guidance on which IIPM products are preferred, and their level ofreliability (MRWA, private communication, 27 November 2015).

Crash modification

An extensive literature review has failed to identify crash modification factors for the installation of IIPMs.However, as they operate in a similar manner to RRPMs, but provide improved delineation over a longerdistance, it is anticipated that crash reductions should be similar, and perhaps slightly higher, than those forRRPMs. However, more research should be done to quantify the in-service benefits of IIPMs.

Treatment life

An extensive literature review has failed to identify any adopted service life values for IIPMs. In the absenceof any such literature, it is assumed that they should have a similar service life as for RRPMs, i.e. five years(Austroads 2010f). It is possible that the service life may be lower, as the electronics in the system mayrequire more frequent servicing.

Also, Styles et al. (2003) report that, in some pedestrian-friendly locations, IIPMs were prone to vandalism ortheft, and that IIPMs may be damaged more frequently due to traffic. Care should therefore be taken inselecting appropriate sites for installation, and ensuring routine maintenance of the markers.


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3. Median Treatments

3.1 Painted MedianPainted medians, also known as flush medians, are a low-cost option that addresses head-on crashes byimproving lateral separation of vehicles and discouraging overtaking (Austroads 2010e).Figure 3.1 andFigure 3.2 show installations of painted medians on curved and straight road sections respectively.

Figure 3.1: Painted median on curve

Source: ARRB Group.

Figure 3.2: Painted median on straight section

Source: Department of Transport and Main Roads (TMR), private communication, November 2014.


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Painted medians are generally preferable to raised medians where the roadway is too narrow to install a raisedmedian (i.e. the associated clearances are not possible), or where the costs are not justified (Austroads 2010g).

Narrowing the road through the installation of medians can also help to reduce travel speeds and encouragedrivers to travel at a more appropriate speed for the environment presented to them. By travelling at lowerspeeds, drivers have more opportunity to avoid a collision, whilst the severity of any crash that may occur isreduced (Austroads 2014c).

Austroads (2010g) specifies that the minimum width for painted medians should be 600 mm. However,Levett, Job and Tang (2009) report that the benefits of painted medians are maximised when they are atleast 1.0 m wide. Cleaver, Jurisich and Dunn (2007) report that variations in median widths between 1.3 mand 3.1 m have negligible impact on the crash rate or severity of crashes.

Therefore, it is suggested that medians should ideally be 1.0 m, after which median width should be basedon the characteristics of the roadway, such as available road width and desirable lane widths.

Figure 3.3 shows a schematic diagram of the layout of a painted median.

When installing painted medians along roads prone to congestion, care should be taken that medians arenot used by drivers to travel through illegally. This may be achieved by keeping median widths narrow or by

installing pavement bars. Pavement bars also improve the effectiveness of the median (Section3.2).

Figure 3.3: Typical layout of painted median

Notes: Based on AS 1742.2-2009. Pavement markers on the outside of an island are unidirectional RRPMs.

Diagonal rows of RRPMs within the marked median should be considered as an alternative to RRPMs along theoutline. Two sets of RRPMs will not normally be required together.

N is generally 12 m for approaches to intersections.

Source: Austroads (2010g).

Crash modification

Roads and Maritime (2015b) suggests a 40% reduction in head-on crashes for painted medians (CMF of 0.60).

Austroads (2010d) adopts a reduction in all crash types of 1520% (CMF of 0.800.85) for the installation ofpainted medians.

Treatment life

Austroads (2010f) adopts a treatment life of five years for painted medians.


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3.2 Pavement Bars

Pavement bars (also referred to as safety bars) are raised blocks located within the painted median, used toaugment the median (Figure 3.4).

Figure 3.4: Example of pavement bars in median


Although traversable, they provide a very strong audio-tactile response, discouraging drivers from crossingthem except in an emergency. They also improve the visibility of the median, particularly in wet conditions(Austroads 2009a). By discouraging drivers from traversing the median, pavement bars also discourageillegal overtaking manoeuvres (AS 1742.2-2009).

This treatment should only be used on roads with 85thpercentile speeds less than 75 km/h. For roads withhigher speeds, RRPMs may be used to augment painted islands instead (AS 1742.2-2009). Pavement barsshould also not be used on roadways with a width less than 6.8 m (Austroads 2009a).

Pavement bars may be useful where raised medians may not be appropriate due to pavement width orlighting issues (AS 1742.2-2009). It is advised that they can be applied at relatively low cost and that they donot affect surface drainage (Austroads 2009a).

When applying this treatment, the needs of motorcyclists and cyclists should be considered. It is suggestedthat bars should be spaced more than 2.0 m apart so they are greater than the typical wheelbase ofmotorcycles2. Use on curves should be avoided so as to prevent the destabilisation of motorcycles at thiscritical point (Austroads 2009a).

Crash modification

An extensive literature search has failed to find any studies as to the effectiveness of this treatment in reducing crashes.

Treatment life

No specific literature could be found identifying a treatment life for the installation of pavement bars. In theabsence of any such literature, it is assumed that this treatment would have a similar service life to raisedprofile centrelines or RRPMs, i.e. five years (Austroads 2010f).

2AS 1742.2-2009 permits shorter separation along the tapered section.


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3.3 Wide Centreline Treatment

Wide centrelines are a type of painted median treatment, also known as the narrow painted median striptreatment (Figure 3.5).

Figure 3.5: Examples of wide centreline treatments

Source: ARRB Group.

This treatment type typically provides a 1 m wide narrow median, increasing the separation of vehicles, butwith negligible effect on vehicle travel speeds (Burdett 2011). Whilst 1 m wide centrelines are the advisedwidth for this treatment, where geometric constraints do not allow for this, narrower wide centrelinetreatments are still expected to provide benefit, albeit reduced, and can be managed on a risk basis.

The addition of raised profile linemarking (Section2.2)increases the effectiveness of this treatment, alertingdrivers should they deviate from their lane (Whittaker 2012).Figure 3.6 shows an example of a widecentreline treatment with raised profile linemarking.

Installation of wide centrelines can generally be achieved within the space available on a two-way undividedroad, e.g. a 1 m wide centreline can be formed by reducing each 3.5 m wide lane to 3.0 m wide (Whittaker2012), or through a combination of narrowing the shoulder and lane widths (Neuman et al. 2003).

However, lane and/or shoulder narrowing can only be achieved if road geometry after narrowing will stillallow trucks and buses to be comfortably positioned away from the wide centreline (Neuman et al. 2003).Lane and shoulder narrowing limits a drivers ability to regain control of an errant vehicle, so practitionersshould consider the occurrence of loss-of-control crashes on the roadway before implementing thistreatment.

Intuitively, reducing the width of the lane will have the effect of concentrating wheel paths, which mayexacerbate rutting in certain situations. Where a road carries significant numbers of heavy vehicles or towedvehicles, reducing the lane width may require further consideration of its impact.

Nevertheless, the benefits of introducing the wide centreline are considered to outweigh the disbenefits ofnarrowing the lanes to 3.0 m to accommodate them (Department of Transport and Main Roads 2013). An

additional benefit of this treatment type is that it encourages lower travel speeds (Neuman et al. 2003).


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Figure 3.6: Layout of painted median outline with raised profile linemarking

Source: ARRB Group.

Neuman et al. (2003) advise that care should be taken when narrowing shoulders to ensure that:

the treatment does not result in greater risk of FSI collisions with roadside objects

there is adequate protection in the shoulder for broken-down vehicles.

The treatment may be further complemented with alternating white diagonal strips and yellow diagonalreflective markers to further highlight the median strip (Whittaker 2012). Alternatively, in Germany the medianis highlighted with green surface markings (Traffic Technology Today 2014).

Figure 3.7: Wide centrelines high lighted by RRPMs and coloured linemarkings respectively

(a) RRPMs

Source: Whittaker (2012).

(b) Green linemarkings

Source: Traffic Technology Today (2014).


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Unlike other median treatments, wide centrelines may be designed to permit drivers to cross into theopposing travel lane to perform overtaking manoeuvres, through the use of broken wide centreline markings(Lilley 2012; Connell, Babic & Pattison 2011). Examples of centreline markings to allow for overtaking fortraffic travelling in either direction and for traffic travelling in one direction only are shown inFigure 3.8.Careshould be taken to ensure that overtaking is only permitted at appropriate locations.

Wide centreline treatments also provide the potential to have wire rope median barriers (WRMB) retrofittedon them (Austroads 2009b). If the intention is for WRMBs to ultimately be added, road designers need toconsider whether a 1.0 m wide median is appropriate. As explained in Section3.6.3,WRMBs are mosteffective when located on medians wide enough to contain barrier deflection within the median. It issuggested that in such circumstances it would be more effective to ensure the median is of sufficient width tocater for the safe performance of WRMBs at the initial point of median installation.

Figure 3.8: Example of wide centreline designed to allow for overtaking for both flows of traffic and one flow of

traffic respectively

(a) Both flows of traffic

Source: DPTI, private communication, December 2014.

(b) One flow of traffic

Source: TfNSW, private communication, January 2015.

Crash modification

Wide centreline treatments have been found to lead to an 80% reduction in head-on crashes (CMF of 0.20),and a 60% reduction of total crashes (CMF of 0.40) (Whittaker 2012).

TfNSW (Private communication, April 2015) have adopted a 50% head-on crash reduction factor for thistreatment (CMF of 0.50).

As an additional benefit, this treatment has been found to lead to a 60% reduction inrun-off-the-road to the left crashes (CMF of 0.40) (Whittaker 2012).

Treatment life

Wide centreline treatments should have a similar treatment life to standard centrelines, i.e. three years forstandard linemarkings, and five years when using raised profile linemarkings (Austroads 2010f).


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3.4 Raised Median

Raised medians, whilst more expensive than painted medians, are often preferred for their conspicuity andphysical deterrent effect in preventing cross-median manoeuvres. Raised medians can also accommodatesignposting, lighting and traffic signal hardware, and may be landscaped, improving aesthetics and restrictingheadlight glare (Austroads 2010g).

Typically, raised medians are more common on urban and semi-urban roads than rural roads.

Figure 3.9 shows an example of a paved raised median, whilstFigure 3.10 shows a grassed raised medianwhich, as well as separating traffic, provides locations for signage and lighting.

Figure 3.9: Paved raised median

Source: ARRB Group.

Figure 3.10: Grassed raised median providing shelter for signs and lighting

Source: ARRB Group.


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When deciding upon the introduction of a raised median, the following factors should be considered(Austroads 2010g), whether:

any artificial lighting needs to be provided

the raised medians are likely to affect drainage and the steps needed to address this

additional roadway space will be required to store immobilised vehicles and for offset to median kerbs.

The kerbing used in raised medians should be semi-mountable and clearly delineated (Austroads 2010g).

Additionally, raised medians on roads prone to congestion should not be appealing to drivers to use as atransit lane (Figure 3.11). This could be achieved by keeping the median width below 2.8 m, or installingfrangible signage posts at regular intervals along the median.

Figure 3.11: Drivers using raised median as transit lane on congested road

Source: Haynes (2009).

Crash modification

Roads and Maritime (2015b) indicates that the installation of raised medians may reduce head-on crashesby as much as 60% (CMF of 0.40).

Schultz et al. (2011) report that installation of raised medians may lead to a 40% reduction in the total crashrate (CMF of 0.60), and a 45% reduction in the FSI crash rate (CMF of 0.55).

Austroads (2010d) indicates a likely 4555% reduction in all crashes (CMF of 0.450.55) with the installationof raised medians.

Treatment life

Austroads (2010f) recommends a treatment life of 20 years for raised medians.


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3.5 Barrier Kerbing on Median

Barrier kerbing may be used to delineate the median and provide a narrow physical obstacle to head-oncrashes (Figure 3.12 toFigure 3.25). This kerb type should ideally be 150 mm high to prevent vehiclestraversing the kerb at low to moderate speeds. This treatment should also only be used on roads with speedlimits of 70 km/h or under, as at higher speeds, the kerb may result in errant vehicles rolling over or

becoming airborne (Main Roads Western Australia 2014).

It is suggested that, when used on medians, an offset of at least 0.3 m should be provided, although 0.6 m ispreferable. As this treatment creates a sense of restriction and does not allow for additional space for reartrailer sway, this kerbing is not recommended on narrow roads or those where a high percentage of traffic isexpected to be heavy vehicles (Main Roads Western Australia 2014).

Whilst being a physical impediment to median crossover, will be unable to prevent most vehicle crossovers.

Barrier kerbing can be formed by bespoke units or pre-cast concrete kerbing units placed back-to-back toform the required profile.

Figure 3.12: Example of median barrier kerbing

Source: Google Maps (2015), New South Wales, map data, Google, California, USA.

Figure 3.13: Further example of median barrier kerbing

Source: ARRB Group.

2015 Google


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Crash modification

An extensive literature search has failed to identify any literature identifying crash modification factors for thistreatment. It is recommended that such investigations be conducted in the future.

Treatment life

In the absence of literature indicating a service life for this particular treatment, it is assumed this treatmentwill have a similar treatment life to other kerb and median treatments, for which Roads and Maritime (2015b)has adopted a 30-year service life.

3.6 Median Barriers

Median barriers minimise the possibility of an errant vehicle crossing into the path of traffic travelling in theopposite direction. It is stated that unless crash history at the site warrants it, median barriers are notnecessary when medians are wide enough or traffic volumes low enough that head-on crash risk should below (American Association of State Highway and Transportation Officials 2011).

Consideration for the use of median barriers should be given based on road environment, anticipated trafficvolumes and an assessment of the risks based on road geometry (Austroads 2010i).

For instance, VicRoads (2003 in Austroads 2010i) specifies that, on freeways with speed limits of 100110km/h, median barriers should be provided:

where the annual average daily traffic (AADT) will exceed 30 000 vpd within 510 years

where the AADT will reach between 20 000 and 30 000 vpd within 510 years and the separationbetween opposing traffic is less than 6 m

where a risk assessment indicates a need for the barrier for any other reason.

A detailed overview of median barriers, including guidance on their selection and installation may be found in

Part 6 of the Austroads Guide to road design (Austroads 2010c).

Barriers used on Australian and New Zealand roads must comply with the Australian and New ZealandStandard AS/NZS 3845.1:2015: Road safety barrier systems and devices part 1: Road safety barriersystems.

Recent research has indicated that, following the installation of median barriers, the crash rate at a site willgenerally increase. However, and aligned with Safe System principles, the severity of such crashes willdecrease, i.e. high-severity head-on crashes resulting from median crossovers will be replaced with morecontrolled crashes of lower severity into median barriers (Chimba et al. 2014).

Road safety barriers dissipate kinetic energy of a vehicle crash into a more manageable form of energy, suchas (AS/NZS 3845.1:2015):

heat through friction

elastic or plastic deformation of components of the barrier and/or vehicle

fracture of components of the barrier and/or vehicle, or both

controlled displacement of the barrier and/or vehicle, such as lifting of the vehicle.

The transfer of energy needs to be achieved in a controlled manner. It is therefore important to ensure thatno unintended snagging of the vehicle occurs, which may lead to unsafe vehicle movements such as rolling,yawing, or excessive deflection into nearby vehicles (AS/NZS 3845.1:2015).


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Depending on the type of barrier and its purpose, median barriers are generally designed to pass crash testsfeaturing private vehicles or small trucks, and impacting at angles between 1525, and at speeds of 50100km/h. Larger vehicle mass or size, impact angles, or impact speeds compromise the barriers ability torestrain the vehicle. This has led some to opine that median barriers should be avoided on tight curves whenpossible (Ross et al. 1993; Transport for NSW 2012). However, such usage is included in the pertinentAustralian Standard AS/NZS 3845.1:2015, with consideration of a reduction in traffic speed or using a

median barrier with a high performance level.When considering the implementation of median barriers, the following issues should be taken into account:

likely crash severity

costs per crash, considering both injury and property damage costs

minimum required width for safe use of barrier

impact of the barrier on sight distance and aesthetics

influence of barrier on drainage

safety of motorcyclists (Section3.6.6)

barrier terminal treatments (Section3.6.7)(Austroads 2010c).

The median width required for installation of a barrier will be dependent on the barrier width and the requiredclearance between the barrier and the traffic edgeline. Required clearance will depend on the expecteddeflection of the barrier during impact with a design vehicle, as well as a nominal clearance at which driverswill feel comfortable driving alongside the barrier (Austroads 2010c).

Ideally, the maximum deflection of the barrier should be less than half the median width in order to preventpenetration of the barrier into opposing traffic (American Association of State Highway and TransportationOfficials 2011) (Figure 3.14). However, median barriers retrofitted on narrower medians have been proved towork successfully when needed (Marsh & Pilgrim 2010).

Figure 3.14: Deflection of errant vehicle by wire rope median barrier

Source: ARRB Group.

Rigid barriers work adequately where there is no room for deflection. However, flexible barriers provide forbetter dissipation of energy, thus reducing the severity of crashes. The disbenefit is that flexible barriers needmore space to deflect without encroaching into the stream of opposing traffic. An increased risk ofpenetration exists with wire rope barriers.

The relative effectiveness of different median barriers in reducing FSI crashes can be viewed inTable 3.1,which presents the FSI crash ratio3for each barrier option.

3The number of fatal or serious injury crashes resulting from running into a crash barrier, divided by the total number of such crashes.


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Table 3.1: FSI crash ratio for safety barrier solu tions

Median barrier option Rural 100 km/h Rural 110 km/h

All types(1) 0.46(2) 0.61(2)

Rigid 0.50(3) 0.50(3)

Semi-rigid 0.60 0.56

Flexible 0.33(3) 0.33(3)

1 There was indication that FSI crash ratios increased with barrier offset from the edge line at about 0.03 per metre.This trend was only demonstrated for semi-rigid and flexible barriers on high-speed roads. The evidence was notconsistent for all barrier types in all speed environments due to the small sample size of crashes into barriers withlarge offset. A relevant scaling factor could be applied to barrier FSI crash ratios if barriers are proposed to be placedsignificantly further away from the edge line than each barrier's typical application range (24 m).

2 The result for all types is based on all available barrier crash data and larger sample sizes. Th us, it may be differentto a weighted average of the results for rigid, semi-rigid and flexible barriers which were based on a smaller data setof manually selected crashes according to the method documented in Austroads (2014b).

3 Based on a sample from Victorian 100 km/h urban freewaysinsufficient data was available on rural roads.

Source: Modified from Table 7.6 of Austroads (2014b).

Crash modification

Elvik and Vaa (2004) indicate that the installation of any type of median barrier on a divided highway shouldresult in a 25% increase in crashes (CMF of 1.25). However, the injury crash rate would reduce by 30%(CMF of 0.70) and the fatal crash rate would decrease by 45% (CMF of 0.55). This study does notdistinguish by crash typeit is likely that the increase in crashes would be primarily due to an increase inrun-off-road into median barrier crashes, whereas a decrease in injury crashes would be attributed to asignificant reduction in head-on crashes, replaced by less severe run-off-road collisions.

3.6.1 Rigid Median Barriers

Rigid median barriers are generally concrete barriers (Figure 3.15), used when space available for deflectionis very limited (Jama et al. 2011). These barriers are generally costly to install (Alba et al. 2014).

Figure 3.15: Example of concrete rigid median barrier

Source: ARRB Group.


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Rigid barriers can be used on medians as narrow as 0.8 m, but, in such cases, the barrier would consumethe entirety of the median space (Austroads 2010i). Ideally, rigid barriers should not be offset more than3.0 m from the edge of a trafficable lane, and never more than 4.0 m. With any greater offset, angles ofimpact would be large, such that severe injuries become more likely (Austroads 2010c).

The minimum length (run) of rigid barriers should be 2030 m. Drainage provisions should be considered toprevent stormwater flooding.

Concrete barriers can also be difficult to see at night-time due to their limited contrast with the roadwaypavement, particularly under wet conditions and/or when drivers are affected by headlight glare (Roads andTraffic Authority 2010). The practitioner should therefore consider including linear delineation on the concretebarrier, particularly on curves (Figure 3.16).

Figure 3.16: Linear delineation of concrete barrier on a curve

Source: ARRB Group.

Crash modification

Tarko, Villwock and Blond (2008) indicate that concrete median barriers will eliminate all cross-mediancrashes (CMF of 0). However, as indicated previously, concrete median barriers do result in an increase inrun-off-road to the right crashes into the barriers, with a 120% increase in single vehicle crashes (CMF of2.2, i.e. more than double). The increased crashes were of much lower severity than the head-on crashes.Whilst Tarko, Villwock and Blond (2008) indicated a slight increase in all casualty crashes, the report doesnot distinguish between severity outcomes.

Due to a likely increase in single vehicle crashes, Elvik and Vaa (2004) deduce that there would be a 15%increase in injury crashes. However, this study does not distinguish between minor and severe injuries, norare separate crash reductions indicated by crash type.

Gan, Shen and Rodriguez (2005) indicate that installation of concrete median barriers should reduce all fatalcrashes by 90% (CMF of 0.10) and injury crashes by 10% (CMF of 0.90).

Treatment life

Austroads (2010f) recommends a treatment life of 30 years for rigid median barriers.


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3.6.2 Semi-rigid Median Barriers

Semi-rigid median barriers provide a degree of deflection to absorb some energy from impact in minimalroad space. These barriers generally fall under three different categories:

W-beams, consisting of W-shaped steel beams facing traffic, supported by steel or wooden posts

thrie-beams, similar to a W-beam but with more corrugations and a higher mounting position. Theyprovide increased rigidity and are typically able to contain larger vehicles

tubular beams of various hollow shapes (e.g. rectangular) supported by posts

steel tubular section on bridge barriers (Jama et al. 2011).

Examples of the most common W-beam barrier in use along a wide and narrow median are shown inFigure 3.17 andFigure 3.18 respectively.

Figure 3.17: W-beam barrier along wide median

Source: ARRB Group.

Figure 3.18: W-beam barrier along narrow median

Source: ARRB Group.

When placing back-to-back semi-rigid barriers on curve medians, consideration should be given to ensurethat the inside barrier maintains sufficient tension in the rail to perform as designed (Austroads 2010c).

Specific manufacturer requirements will apply.The minimum length of installation for semi-rigid barriers should typically be 30 m (Austroads 2010c).


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When installing semi-rigid barriers near kerbs, they should either be installed within 200 mm of the kerb orsome distance behind to avoid the kerb/barrier configuration from causing vehicles to vault over the barrier(Austroads 2010c).

Crash modification

Alluri, Haleem and Gan (2013a) report that W-beam barriers prevent 95% of cross-median crashes (CMF of0.05), including almost 100% of crashes involving cars (CMF of ~0.00) and 90% of crashes involving lighttrucks (CMF of 0.10). The effectiveness for medium and heavy trucks was lower with reductions of 80%(CMF of 0.20) and 75% (CMF of 0.25) respectively.

Treatment life

Austroads (2010f) recommends a treatment life of 30 years for semi-rigid median barriers.

3.6.3 Wire Rope Median Safety Barr iers

Wire rope median safety barriers (WRMBs), also called wire rope safety fences (WRSF) or cable barriers,are essentially flexible crash barriers. The barrier uses steel cables supported by collapsible posts to absorbenergy, contain errant vehicles and redirect them back towards their intended path. The system was firstintroduced to New South Wales in 1991, and is now in use in all jurisdictions in Australia (Austroads 2009b).

WRMBs as a means to prevent crossover crashes may be applied on a median or along wide centrelines(Figure 3.19)(Austroads 2009b). When undivided roads are upgraded to wide centrelines with WRMBs,traffic has been found to travel further from the centre of the road, such that vehicles are both physicallyrestrained, and also have a greater buffer to avoid head-on and run-off-road to the right crashes (Marsh &Pilgrim 2010).

Figure 3.19: WRMB in wide ce

AP-R519-16 Guidance on Median and Centreline Treatments to Reduce Head-On Casualties

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