Determining safety aspects of Differential Speed Limit on Indian Expressway

Abstract

Optimization of operating speed limit on any class of road is the biggest task faced by the transportation experts. A variety of speed control or management techniques are available all around the globe to minimize the frequency of over-speeding or for increasing the acceptability of the posted speed limit. In this study, a comparison is carried out between Uniform Speed Limit (USL) and Differential speed Limit (DSL) on an Expressway in India, using microsimulation package PTV VISSIM. In USL, a single speed limit is implemented for all class of vehicles whereas DSL strategy have two distinct speed limit for two different class of vehicles i.e., passenger carrying vehicles and goods carrying vehicles. Multiple Key Performance Indicators (KPIs) were considered. Results suggested that DSL seems to be the better strategy on the roads accommodating high speeds like Expressways under heterogenous conditions. Four out of five KPIs were showing the results in favor of DSL strategy in comparison to USL strategy. KPIs like speed variance, Road Safety Index (RSI), no. of vehicles having Deceleration-Rate-to-Avoid-Collision (DRAC) > 3.35 m/sec2 and no. of lane changes were showcasing better results in case of DSL strategy in comparison to USL strategy.