The early life skid resistance of asphalt surfaces

For some years it has been suspected that new asphalt surfacings may have different skid resistance properties to surfaces have aged in service. This is thought to be due to the presence of a film of bitumen binder on the new surface that is eventually removed by weathering and traffic. New surfacings that are quicker to lay and generate less tyre noise have been introduced in recent years but there have been concerns that the risk of early-life skid resistance problems and the time that any effects last, may have increased. This study included an initial investigation of the effects of speed on both wet and dry skid resistance on new Stone Mastic Asphalt (SMA), followed by further phases in which a reduced range of measurements was made on a greater number of sites in order to cover a wider range of surfacing types of different ages, roads, tyres and traffic conditions. The primary purpose of the work was to understand better the general skid resistance effects and to determine how long they last. It was not designed to compare the performance of different proprietary or generic materials. Interim advice based on early observations from this work was introduced by Highways Agency in 2003. This report provides an overview of the results of the various tests and discusses the phenomena observed and the implications for accident risk. The study concludes that in most circumstances, on most roads, the increased risk of accidents associated with these effects on new surfacings is likely to be small but further work is needed to identify the best ways of reducing risks on the relatively small number of sites where this might be necessary.