Simultaneous equation Tobit analysis of arterial road crash rates

Abstract

The objective of this study was to identify the influencing factors of road traffic crash rates from the perspective of access management techniques in urban areas. The target areas are located in the Las Vegas metropolitan area in the USA and 19 arterial routes were selected. To address the interdependency between crash rates and travel speeds and left-censored issue, simultaneous equation Tobit models are presented. The structure of the model addresses the left-censored issue for the segments while the simultaneous equation models treat the endogeneity issue between crash rates and travel speeds. The results indicate that there is a strong interdependency between crash rates and travel speeds. Segment length, driveway density, median (central reservation) opening density, posted speed limit and annual average daily traffic per lane were found to be statistically significant factors that influence both crash rates and travel speeds on segments. Moreover, crash rates are significantly influenced by two-directional median opening density.