Application of generalized estimating equations for crash frequency modeling with temporal correlation

Abstract

Traditional crash frequency modeling uses crash frequency data averaged across multiple years. When data size is small, crash data in each year are used in the modeling to extend the size of the samples. The extension of sample size could create a temporal correlation among crash frequencies of the different years, which could affect the modeling accuracy. The primary objective of this study is to evaluate the application of the generalized estimating equation (GEE) procedures to account for the temporal correlation in the longitudinal crash frequency data. Four-year crash data at exit ramps on a freeway in China were collected for modeling. Based on the same data, traditional generalized linear models (GLMs) were estimated for model comparison. Results showed that traditional GLM underestimated the standard errors of coefficients for explanatory variables. The GEE procedure with an exchangeable correlation structure successively captured the temporal correlation among the crash frequencies of the different years. The GLM with GEE outperformed the traditional GLM in providing a good fit for the crash frequency data. Results of this study can help researchers better understand how various factors affect the crash frequencies at freeway divergent areas and propose effective countermeasures.

Analysis of Crash Rates at Freeway Diverge Areas using Bayesian Tobit Modeling Framework

“…There are many studies focusing on the safety evaluation of freeway exit ramp areas (1)(2)(3)(4)(5)(6)(7)(8)(9)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36). Previous studies developed various CPMs to relate crash frequency at exit ramp sections to traffic volume and ramp design elements among others.…”

“…To better understand the risk factors affecting crashes at freeway diverge areas, analytical tools need to be developed that can aid transportation safety professionals in mitigating crashes. Previous studies have developed several crash prediction models (CPMs) to evaluate the safety performance of freeway exit ramp areas (4)(5)(6)(7)(8)(9). However, none of these studies have focused on crash rates analysis.…”