Skid Resistance

Loss of control through skidding can be a significant factor in many crashes (especially when the road is wet). Particular attention should be paid to the skidding resistance properties of the carriageway surface at areas where braking commonly occurs such as on the approaches to intersections, pedestrian crossings and on bends.

Poor skid-resistance can occur when the road surface becomes worn (aggregate becomes polished) under the action of traffic, or temporarily if there is a build-up of oil or debris on the road or if road drainage is poor. There are two main options for treatment of low skid resistance:

Retexturing This method includes the mechanical reworking of the existing surface to improve its frictional characteristics and therefore the resistance to skidding. Typically involves the removal of material from the road surface. Methods include diamond grooving, shot-blasting, bush hammering, high velocity water blasting.

Resurfacing These include relatively low cost thin surfacing treatments that not only improve the surface texture and resistance to wet road skidding but can also seal the surface against water penetration and arrest disintegration of the existing road surface.

  • Surface dressing for example, uses a bitumen emulsion sprayed onto the road surface followed by a layer of chippings with a high Polished Stone Value (PSV).
  • High friction surfacing (HFS) utilizes an extremely hard wearing aggregate (with a high PSV) that provides good skid resistance. Applied using thermoplastic (hot-lay) or rosin ester (cold-lay) resin.

    • Improved safety for roads where a lot of crashes happen, especially in wet weather.
    • Can help to prevent both rear-end and run-off road crashes.
    • Resurfacing provides an opportunity to fix other road surface problems, such as crossfall and rutting.
    • Provides the opportunity for adding or replacing road surface delineation such as painted markings or reflective road studs.
    • Can extend life of pavement surface.
    • Retexturing has environmental benefits over some traditional hot mix asphalt resurfacing. Typically lower cost and lower energy solution.
    • Often quick and repeatable treatments with low traffic disruption. In most cases roads can be driven on immediately after application.
    • Skid resistance improvements gained by retexturing and resurfacing will lessen over time, especially on roads with lots of heavy vehicle traffic and in tropical climates. As such, regular monitoring of skid resistance is important.
    • The skid resistance of the entire road surface (right up to the edge) should be maintained for the safety of bicycles and other slow-moving vehicles.
    • Warning signs should not be considered a solution to the problem of poor skid resistance. Warning signs can be used temporarily, until other solutions are carried out.
    • Existing road surface must be sound, therefore pre-patching and repairs may be necessary prior to application.
    • These treatments will not typically add any strength to the road pavement.

    Benefits

    • Improved safety for roads where a lot of crashes happen, especially in wet weather.
    • Can help to prevent both rear-end and run-off road crashes.
    • Resurfacing provides an opportunity to fix other road surface problems, such as crossfall and rutting.
    • Provides the opportunity for adding or replacing road surface delineation such as painted markings or reflective road studs.
    • Can extend life of pavement surface.
    • Retexturing has environmental benefits over some traditional hot mix asphalt resurfacing. Typically lower cost and lower energy solution.
    • Often quick and repeatable treatments with low traffic disruption. In most cases roads can be driven on immediately after application.

    Implementation issues

    • Skid resistance improvements gained by retexturing and resurfacing will lessen over time, especially on roads with lots of heavy vehicle traffic and in tropical climates. As such, regular monitoring of skid resistance is important.
    • The skid resistance of the entire road surface (right up to the edge) should be maintained for the safety of bicycles and other slow-moving vehicles.
    • Warning signs should not be considered a solution to the problem of poor skid resistance. Warning signs can be used temporarily, until other solutions are carried out.
    • Existing road surface must be sound, therefore pre-patching and repairs may be necessary prior to application.
    • These treatments will not typically add any strength to the road pavement.

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    Treatment Summary

    Costs
    Low to medium
    Treatment life
    5 years - 10 years
    Effectiveness
    25-40%

    References

    • iRAP Road Attribute Risk Factors - Skid Resistance.
    • iRAP Road Attribute Risk Factors - Road Condition.
    • Towards Safer Roads, p114-115.
    • Surveyor article - Road surface retexturing
    • Austroads (2002-07) Road Safety Risk Assessment Project.
    • Elvik, R., Hoye, A., Vaa, T. and Sorensen, M (2009) The Handbook of Road Safety Measures, 2nd edn, Emerald Group, United Kingdom.
    • Ogden, K. W. (1996) Safer Roads - A Guide to Road Safety Engineering. Avebury Technical, Ashgate Publishing Limited, Grower House, Croft Road, Aldershot, England.
    • DfT Design Manual for Roads and Bridges, Vol.7. HD 28/04 Skid Resistance
    • DfT Design Manual for Roads and Bridges, Vol.7. HD 37/99 Bituminous Surfacing Materials and Techniques
    • TRL Report 298. Mechanical retexturing of roads - A study of processes and early-life performance.
    • TRL Report 299. Mechanical retexturing of roads - An experiment to assess durability.

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