Identifying Access Management Factors Associated with Safety of Urban Arterials Mid-Blocks: A Quantile Structural Equation Model Approach

The identification of factors that influence crash rates have been studied, but most existing methodologies adopt mean regression models to estimate the parameters. This study presents the quantile structural equation model as an alternative for analyzing crash rate in urban arterials. A two-step estimation procedure in which the simultaneous equations model accommodates the endogenous relationship between crash rate and travel speed, while the quantile regression estimates various quantiles of crash rate instead of the mean regression and accounts for the heterogeneity attributed to unobserved factors. The quantile approach is able to provide more comprehensive information about the impact of access management and other influencing factors on crash rate compared to the general simultaneous equations model. Crash data from the Nevada Department of Transportation is employed to illustrate the performance of proposed model. The proposed model reveals detailed information in terms of different quantiles and improves the prediction accuracy.