Influence of Horizontal Curve Geometry on Operating Speeds on Four-Lane Divided Highways Under Heterogeneous Traffic Conditions

Road geometry is regarded as one of the most important factors influencing vehicle speed, raising concerns about disparities between design and operating speeds on different highways. Several studies have focused on predicting operating speed on two-lane highways, only a few studies have been done on multi-lane highways. The objective of the study is to develop operating speed prediction models by considering horizontal curve geometric parameters of four-lane divided highway. Field data were collected at various sections of horizontal curve in southern parts of national highways in India. Section geometry data was measured with the help of total station equipment. The distribution analysis was carried out for speed of individual vehicles to understand the nature of speed in mixed traffic conditions. Speed data was analyzed and it was found that the individual vehicle class speeds followed either normal or log-normal distribution, while, mixed traffic speed data followed more than one type of statistical distribution. In the case of mixed traffic condition, the Beta and Weibull distributions were commonly observed as best fit. Models were developed to estimate operating speed on the basis of geometric characteristics. The present study developed two different models with variables 1/R and Ln(R) for predicting operating speeds. Differential operating speed models (∆V85) are also proposed in current study to perceive speed variation of vehicles while traversing different points on the curve. The developed models were compared with existing models in the literature and validated with field data. The proposed models are easier for traffic engineers to anticipate the operating speed and set speed limit on multi-lane highways. © 2022, The Institution of Engineers (India).