Modelling Operating Speeds for Multilane Divided Highways

Abstract

Different geometric parameters (e.g., radius, curve length and preceding tangent length) affects vehicle speed in horizontal curve. Inconsistency in driver’s speed selection may lead to unsafe situation at horizontal curve. The differences between operating speed of successive elements and deviation with design speed of single element have been used as a measure to evaluate geometric design consistency and safety. Researchers have studied speed behaviour considering strong lane discipline to predict preferred vehicle operating speed in two lane highways. However, studies considering weak lane discipline to predict operating speed for multi-lane divided highways are limited. Therefore, in this study, passenger car and heavy vehicle speed data at the starting and centre of ten horizontal curves in a four-lane divided highway are collected. The 85th percentile speeds at eight sites are analysed to develop a linear speed prediction model. Curve length is found to be the only explanatory variable in the model developed for location at the starting of a curve. Whereas, radius is found as the explanatory variable to predict speed at centre of the curve. The developed models are validated at two different sites. Statistical analysis shows that I-value is lesser than 0.2, which confirms the acceptability of the proposed model.