Effect of horizontal curve geometry on vehicle speed distribution: a four-lane divided highway study

Abstract

ABSTRACT Poor coordination between geometric elements of horizontal curves can lead to unsafe speed. This study evaluated the effect of horizontal curve geometry on vehicle speed distribution for a four-lane divided highway and developed prediction models for mean speed and standard deviation. Spot speed data of passenger cars (PC), heavy commercial vehicles and light commercial vehicles were collected at 24 horizontal curves. Statistical analysis of the speed data of randomly selected 10 sites revealed PC as the critical vehicle category. Hence, the effects of horizontal curve geometry on PC speed were analyzed and radius was identified as the most influencing parameter. Radius beyond 400 m had similar influence on speed distributions. Appropriate models were developed using regression analysis. Degree of curvature was found as the most significant predictor. Benefits of the proposed models over traditional 85th percentile speed in designing and evaluating horizontal curves for consistency and safety were discussed.