Lateral friction demand on roads with coincident horizontal and vertical sag curves

Abstract

Rural highway crash analyses have shown that the majority of accidents occur on horizontal curves where the vehicle is exposed to lateral forces, which increase the probability of skidding. Moreover, in cases of compound alignments where curves from the road's horizontal alignment are overlaid with constant grades or vertical curves, the probability of skidding increases due to the increase of the longitudinal force on the vehicle. In this research, by utilising vehicle multi-body simulation modelling, several scenarios are defined to assess the impact when horizontal curves are combined with vertical sag curves for three different kinds of vehicles (sedan, sports utility vehicle and truck). For various speed values, the maximum lateral friction demand between the road surface and vehicle tyres is calculated. Finally, by using regression analysis, a model is presented according to the inputs and outputs of the simulation modelling to determine the maximum lateral friction demand created in various conditions. The results of this research indicate that the maximum lateral friction between the road surface and vehicle occurs when the lower part of the sag vertical alignment is located in the middle of horizontal curve.