accident frequency in the U.K. (Hosking 1986). He observed that on most of the geographical regions and groups of roads studied, changes in dry-road skidding rates were related to wet-road skid resistance. However, he attributed this apparent correlation at least in part to misreporting of roads in the accident statistics as dry when they were actually damp.
Since then, in-service skid resistance standards have been enforced since 1987, and the vast majority of roads (especially the main highways) now have good wet skid resistance and macrotexture. It has been found (as do the police investigating crashes) that the measured dry friction (locked-wheel) is pretty consistently similar across the network and that wet friction is much more variable. Therefore, it is recommended that a PFMP focus on the worst case of wet road conditions.