MODELLING LATERAL PLACEMENT AND LATERAL CLEARANCE DURING PASSING MANOEUVRES

Passing manoeuvres are inevitable on two lane highways with heterogeneous traffic because of the speed differential prevailing in the traffic flow. It is one of the most complicated as well as unsafe manoeuvre observed on two-lane two-way roads. Among the various parameters which influence safe passing, lateral placement and lateral separation of vehicles plays a major role. Lateral placement of a vehicle during overtaking manoeuvres, are influenced by traffic characteristics namely, traffic volume and composition, speed of the overtaking vehicle and opposing vehicle, shoulder type and condition etc. The lateral interactions between vehicles involved in passing manoeuvring in a heterogeneous traffic environment have significant influence in traffic performance and safety. This paper examines the lateral spacing of vehicles during passing manoeuvring in terms of lateral placement of overtaken vehicle and lateral clearance between overtaken and passing vehicle. In this study, the lateral placement of each class of vehicle and how it is influenced by traffic volume and composition is examined. As evident from the results of the study the type and composition of vehicles is having an influence on passing characteristics. Hence to understand the effects of numerous traffic and geometric parameters on lateral placement, a linear regression model has been developed. To extensively study the passing manoeuvres under heterogeneous traffic, a simulation model is also calibrated to assess the effect of various traffic parameters. The simulation study makes use of VISSIM software, and an overtaking simulation model was developed and calibrated. The findings indicate that during passing manoeuvres, the majority of the vehicles take a lateral position nearly in the middle of the road. When the truck composition changes, there is a significant change in the number of passing manoeuvres and speed of passing manoeuvres.