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9/10/2014 https://www.mainroads.wa.gov.au/BuildingRoads/StandardsTechnical/RoadandTrafficEngineering/TrafficManagement/RoadsideAdvertising/Pages/

https://www.mainroads.wa.gov.au/BuildingRoads/StandardsTechnical/RoadandTrafficEngineering/TrafficManagement/RoadsideAdvertising/Pages/Append 1/4

Home Building Roads Standards and Technical Road and Traffic Engineering Traffic Management

Roadside Advertising Appendix B

Appendix BDocument No: 67-08-4C Revision: 1 Date am ended: 04-Jan-2002

The information below is under development and is provided for information purposes only.

Main Roads Western Australia reserves the right to update this information at any time without notice. If you have any questions or comments

please contact Ed Jordanby e-mail or on (08) 9323 4604.

To the extent permitted by law, Main Roads, its employees, agents, authors and contributors are not liable for any loss resulting from anyaction taken or reliance made by you on the information herein displayed.

Revision Register

Ed/Version Number Clause Number Description of Revision Date

ISSUE 1 ALL GUIDELINE DEVELOPED 04/01/02

Table of Content

APPENDIX B - Method for Determination of the width of the Clear Zone

General

Factors Influencing the Clear Zone

Determination of Clear Zone Requirements

Opportunities to Reduce Lateral Clearances

Figures

APPENDIX B - Method for Determination of the width of the Clear Zone

General

The clear zone concept adopted by Main Roads is a universally accepted means of diminishing the risk of errant vehicle collision with

roadside objects and also of maintaining the effectiveness of traffic sign or a traffic control signal.

While the concept draws on a wide range of experience and res earch, engineering judgement s hould also be applied in the determination of

lateral position requirements. These guidelines s hould be regarded as a supplement to aid in exercising this judgement and not as a

substitute for it.

Factors Influencing the Clear Zone

The variables that influence the determination of the clear zone for Advertising Devices include the following:

speed environment;

roadside cut/fill s lopes;

road curvature;

presence of physical devices that limit or prevent errant vehicle incursion (e.g. barrier rail or steep cutting); and

the nature of transport infras tructure, if any, to which the device may be attached.

Once these variables are established, a simple procedure enables the clear zone to be determined.

Determination of Clear Zone Requirements

The influence of the above-mentioned variables on the width of the clear zone is determined by assessing the device site in accordance with

the following:

The clear zone is measured by extending a horizontal plane from the edge of the travelled way to the edge of the device, as indicated in

Figure B1.

Figure B2 is used to establish the required clear zone distance for Advertising Devices located on straight roads, given a designated

speed environment and the slope of the roadside.

A combination of Figures B2 and B3 is used when the device is located on a curve in the road alignment. The horizontal curve multipli er

established from Figure B2 recognises the higher risk and larger encroachment distance for errant vehicles on curved road alignm ents.

A combination of Figures B2 and B4 is used to asses s the influence of cut height and slope on traversability when the device is located on

a cut slope.

Figures B5 and B6 provide examples of the influence of cut height and slope on traversability and opportunities to reduce lateral clearance.

Figure B7 provides an example of clear zone calculations on variable slopes. On such slopes, it is necessary to approximate the

contributory influence of each slope element, noting that non-recoverable fill slopes (i.e. slopes steeper than 4:1) are disregarded in the
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calculation.

Opportunities to Reduce Lateral Clearances

The requirements outlined in this Appendix also present a number of avenues via which the base clear zone distance (i.e. the clear distance

determined for a device located adjacent to a flat roadside) may be reduced. Given the significant advantages in placing Advertising Devices

as close as possible to the observer's line of sight, it is expected that the following avenues will be actively pursued:

Case (i) - Device located on a suitable cut slope:

The clear zone distances determined from Figure B2 (for speed environments exceeding 60 km/h) converge to a m inimum permiss ible

distance of 4.5m for traversable cut slopes steeper than 2:1. As is apparent from Figure B2, advantages accrue when cut slopes steeper than

6:1 are encountered, in that Advertising Devices m ay be located closer to the travelled way.

See diagrammatic example at Figure B6 - Case (i).

Case (ii) - Devices with a lateral offset of the device face from the supporting structure and clearance between the ground and the device face

exceeding 5.4m:

The clear zone distances determined from Figure B2 (for speed environments exceeding 60 km/h) converge to a m inimum permiss ible

distance of 4.5m to the edge of the device face, where the clearance between the ground and the device face exceeds 5.4m. The clear zone

requirements to the supporting structure still apply.

See diagrammatic example at Figure B6 - Case (ii).

Case (iii) - Devices located behind a non-traversable cut slope or barrier:

Non-traversable cut slopes or barriers (e.g. guard rail) also potentially enable the device to be located within the calculated base clear zone.

Figure B4 provides a means by which cut slope traversability can be established. As with Case (ii), this relaxation limits the minimum clear

separation between the travelled way and the edge of the device face to 4.5m.

The installation of a barrier on steep fill slopes for the sole purpose of enabling the relaxation outlined in Case (iii) is not permissible, except

where the barrier results in lower hazard potential than existed prior to its installation. An engineering risk assessment, in accordance with

recognised best practice, is required in support of applications that propose the installation of a traffic barrier. The cost of barrier installation

in these circumstances s hall be borne by the applicant.

See diagrammatic examples at Figure B5 and at Figure B6 - Case (iii).

Case (iv) - Devices attached to transport infrastructure:

Clear zone requirements do not apply for devices attached to transport infrastructure such as bus passenger shelters and seats, overhead

road bridges and pedestrian overbridges.

Figures

B1: Clear Zone Base Parameters

B2: Clear Zone Distance Curves for Straight Roads

B3: Clear Zone Horizontal Curve Adjus tment Factors

B4: Influence of Cut Height and Slope on Traversability

B5: Examples of Influence of Cut Height and Slope on Traversability

B6: Examples of Opportunities to Reduce Lateral Clearance

B7: Examples of Clear Zone Calculations on Variable Slopes


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Figure B1 - Clear Zone Base Parameters

Figure B2 - Clear Zone Distance Curves for Straight Roads

Clear zone curves adapted from AASHTO "Roadside Design Guide" and Queensland Transport draft Technical Guideline - "Identification,

Prioritisation and Treatment of Roadside Objects".

This diagram does not identify all s ituations. For curved roads on cut slopes , the clear zone is determined by using the above diagram in

conjunction wi th Figure B3 ( Clear Zone Horizontal Curve Adjustment Factors), Figure B4 (Influence of Cut Height and Slope on Traversab ility)

and Figure B5 (Examples of Influence of Cut Height and Slope Traversability) and Figure B5 (Examples of Influence of Cut Height and Slope

Traversability). For roads on fill slopes, the diagram is used in conjunction with Figure B7 (Examples of Clear Zone Calculations on Variable

Slopes.)

Figure B3 - Clear Zone Horizontal Curve Adjustment Factors

Notes

Horizontal curve multipliers adopted from AASHTO " Roadside Design Guide". Permission limits are based on a 'comfortable' lateral

acceleration of 4.9m/s2(.2g) AUSTROADS "Guide to the Geometric Des ign of Rural Roads ".

Irrespective of the proposed device being located on a horizontal curve that falls within the ''permitted' region of the graph, consideration shall

also be given to any site accident history before approval is given for the erection of a device on a horizontal curve.

Figure B4 - Influence of Cut Height and Slope on Traversability


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Figure B5 - Examples of Influence of Cut Height and Slope on Traversability

Figure B6 - Examples of Opportunities to Reduce Lateral Clearance

Figure B7 - Examples of Clear Zone Calculations on Variable Slopes

Clear zone distances for variable slopes up to 4:1 may be averaged to produce a composite clear zone distance. The "weighted average" of

the slopes in the above example is determined by dividing the total slope height (5x0.1+8x0.2) into the sum of the horizontal components

(8+5). The result of the calculation (8+5)/(5x0.1+8x0.2) is 6.2. For 100km/h speed environment the clear zone required for this "average" 1:6.2

slope = 10m. (Note that of the resultant clear zone requirement varies significantly from the sum of the horizontal components, an iterative

procedure should be adopted).

The 3:5:1 slope in this example is non recoverable and consequently does not contribute to the total clear zone requirement. The required

clear zone is determined from Figure B2 using the steepest recoverable slope before or after the non recoverable slope (i.e. the 8:1 slope).

For the 100km/h speed environment the 8:1 slope requires a 9m clear zone, of which the upper (10:1) slope contributes 5m. An additional

4m is subsequently required at the base of the non recoverable 3.5:1 slope as s hown.

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