Road surfaces on approaches to pedestrian crossings in the UK have a different composition, presumably to allow cars to stop quickly. What is this surface and how does it work? Why aren’t all roads constructed using it?
• The road surfacing referred to is a thin layer of , or chippings of such fixed to the base of the road by epoxy resin. The calcined bauxite retains its roughness far longer than normal road surfacing, which eventually becomes shiny and polished by vehicle tyres. This layer allows vehicles to decelerate and stop more quickly without skidding. In the late 1960s, Shell marketed the earliest examples of calcined bauxite as Shellgrip.
In 1970, I was a graduate working with the (GLC). One of my tasks was to investigate the effectiveness of this treatment, which the council had installed at a number of sites with high accident levels. Because the treatment was significantly more expensive than normal resurfacing, the council naturally wished to know whether the additional expense was justified.
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By comparing accident records for the three years before the surfacing was installed with those in the years after, I demonstrated that the treatment was a highly effective way of reducing accidents resulting in injury, as well as the more common damage-only, rear-end shunts between vehicles that frequently happen at pedestrian crossings and junctions with traffic lights. The potential saving was so great that it justified applying the treatment to virtually all similar sites, which the GLC did over the following years.
“The rough road surface is a highly effective way of reducing accidents at pedestrian crossings”
Your correspondent wonders why the treatment is not applied universally. The answer is mainly that the cost would be prohibitive. Also, if the whole network was surfaced this way, vehicle tyres would undoubtedly wear out much faster because of the higher friction created between the tyres and the road surface.
Roger Waddington, Banwell, Somerset, UK
• Your questioner is referring to the high-friction calcined bauxite material that is applied by hand to the road surface in areas where anti-skid properties are a priority, such as at pedestrian crossings or on sharp bends, where the accident rate is high.
It works because the high-friction material offers greater grip for a car’s tyres.
There are three reasons why this material isn’t used everywhere. First, all main road surfaces are checked for adequate skid resistance by local authorities on a routine basis, and as conventional road design normally meets skid resistance specifications without the application of a high-friction dressing, its use is restricted to areas of high stress.
Secondly, its use at pedestrian crossings serves another purpose – the different colouring provides a visual reminder to the driver of a hazard ahead.
Finally, the downside of this material is that road authorities have to maintain it, as it can wear off in patches, causing a hazard that requires remedial action at further cost, so its use is restricted to areas justifying the additional expense.
Alistair Donald, Service Manager (Construction Operations), Transportation & Environmental Services department, Fife Council, Glenrothes, Fife, UK