Developing Safety Performance Functions and Crash Modification Factors for Urban Roundabouts in Heterogeneous Non-Lane-Based Traffic Conditions

Abstract

This study aims to develop safety performance functions (SPFs) and crash modification factors (CMFs) for the safety assessment of roundabouts as a whole and their components, especially at entry, exit, and circulating lanes. This study uses historical crash data collected over five years (2015–2019) from 21 roundabouts (78 approaches) situated in some of the major cities in India. SPF and CMF models were developed using negative binomial and cross-sectional approaches. Results show that the percentage of motorized two-wheelers, average daily traffic, central island diameter, entry angle, weaving width, departure width, number of lanes at approach, exit angle, exit width, posted speed limit, weaving length, circulating roadway width, road surface condition, number of circulatory lanes, central island height, and number of legs contribute to the crash occurrence in the roundabout vicinity. In addition to this, circulating roadway width, average daily traffic, and posted speed limit are the most influencing risk factors across the entire roundabout vicinity. Furthermore, an interesting fact is that, given the asymmetrical impact of geometric and traffic factors, the overall crash rate varies across roundabout segments. The findings of this study may be useful for updating the current design guidelines for roundabouts, considering the safety perceptive. Besides, the proposed SPF and CMF tools could be used to investigate the likelihood of crashes at roundabouts. Moreover, this model would help safety experts to implement adequate safety treatment in the vicinity of roundabouts under heterogenous non-lane-based traffic conditions.