Abstract
The objective of this study is to identify the influencing factors of crash rates from the perspective of access management techniques in urban areas. The target areas are located in the Las Vegas Metropolitan area, and 19 arterials are selected. In order to address the interdependency between crash rates and travel speeds, and left-censored issue, a tobit model with endogenous variable is presented. The structure of the tobit model addresses the left-censored issue for the segments meanwhile the endogeneity issue between crash rates and travel speeds is explained. The results indicate that there is a strong interdependency between crash rates and travel speeds. The segment length, driveway density, median opening density, posted speed limit and AADT per lane are statistically significant factors that influence crash rates on segments, moreover, crash rates are significantly influenced by two-directional median opening density.
Highlights
The most widely used approach to study the influencing factors of crash occurrence is to analyze the crash frequency on roadway segments during a specified period of time
The way in which the crash rates are used is because crashes per 100-million vehicle miles travelled is a continuous variable instead of the non-negative integer used for discrete crash event over some period, but there might be no-crash-occurred for some roadway segments during the observation period, so that the data will be left-censored at zero
Where N is the number of observations, Yi is the dependent variable, Xi is a vector of independent variables, b is a vector of estimable parameters, bXi denotes the scalar product of two vectors, and fi is a normally and independently distributed error term with zero mean and constant variance v2
Summary
The most widely used approach to study the influencing factors of crash occurrence is to analyze the crash frequency on roadway segments during a specified period of time. Crash rates (such as the number of crashes per million vehicle miles travelled) have been considered as one standardized measure of roadway safety [2]. The way in which the crash rates are used is because crashes per 100-million vehicle miles travelled is a continuous variable instead of the non-negative integer used for discrete crash event over some period, but there might be no-crash-occurred for some roadway segments during the observation period, so that the data will be left-censored at zero. In order to deal with the Promet – Traffic&Transportation, Vol 25, 2013, No 3, 217-224
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