Abstract

One of the main challenges in geometrical design of highways is to define the braking distance required by the driver-vehicle system. For a specific design speed, the braking distance mainly depends on the friction between the tyre and the road. Design standards define friction values given a certain speed. Design values are not, however, correlated directly to skid resistance and macrotexture of the road surface. The present study proposes a procedure to estimate skid resistance and macrotexture thresholds in terms of the design friction of a road. The procedure is developed using a harmonisation function based on the international friction index (IFI). Using the proposed procedure, skid resistance and macrotexture thresholds that fulfil design friction requirements were defined. The results showed that thresholds are not unique; instead, a set of skid resistance-macrotexture values which fulfil the design friction can be defined for each design speed. Consistency between geometrical design and the characteristics of a road surface can be evaluated with the proposed procedure. The procedure can be applied for any design standard and for any skid resistance and macrotexture measuring device.