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.

Incorporating Horizontal Curves and Roadway Geometry into the Automated Updated Grade Severity Rating System

“…Tavassoli Kallebasti et al ( 17 ) computed the tire–road side friction demands for compound alignments created by horizontal curves on various longitudinal grades using a simulated model. They concluded that the effects of grades for trucks and sedan passenger cars are much more critical than for sports utility vehicles (SUVs).…”

“…The authors of the study recommended placing warning signs a specified distance before the beginning of the horizontal curve to reduce the speed of vehicles entering a combined curve (longitudinal grade coupled with horizontal curve) before entering the danger zone ( 17 ).…”

“…Crash analyses of highways running through rural areas indicate that the vast majority of accidents take place on horizontal curves, during which time the vehicle is subject to lateral forces, increasing the probability of skidding ( 17 ). For downgrades featuring compound alignments in which curves from the roads’ horizontal alignment are overlain with constant grades or vertical curves, the probability of skidding increases as a result of increases in longitudinal forces on the vehicle.…”

“…They concluded that the effects of grades for trucks and sedan passenger cars are much more critical than for sports utility vehicles (SUVs). The models based on which side friction demand is delivered for cases of sedan passenger cars, SUVs, and trucks are outlined in the equations below ( 17 ):…”

“…Apart from this, the motion of the vehicle is examined independently in the tangential and lateral direction of travel, whereas the restrictions for which the various components interact are ignored. At the same time, heavy vehicle dynamics are practically ignored when evaluating the safety performance of a highway alignment ( 17 ).…”