Following on from my article in the last issue about the lack of a definite link between PSV and SCRIM (skid resistance), it follows that aggregate choice for surfacing, and surface treatments, poses difficulties for the designer. Highways England (HE) provide a table in HD36/06 linking hazard categories and traffic levels, but the categories are wide and, for most risk categories, there are 2 or even 3 choices. At low traffic levels the new RN39 (from TRL or the RSTA) has subdivided the 0 to 250 cv/lane/day category which is helpful for lightly trafficked roads.
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