Abstract
Road accidents involving heavy duty trucks have long been of concern but detecting the impact on accidents of various policies is typically challenging. The objective of this study is to understand if there was a change in accident rates on a busy freight corridor (the I-710 freeway in Los Angeles County, California) connecting the Ports of Los Angeles and Long Beach to nearby intermodal rail, trans-loading facilities, and warehouses after the implementation of the PierPASS program on July 23, 2005. The authors analyzed 2,043 accidents that occurred in 2005 on the I-710 freeway; approximately 27.8 percent of these accidents involved trucks. The authors estimated a three stage hierarchical Bayesian change point model with MCMC developed by Carlin et al. (1992) to evaluate whether the implementation of the PierPASS program resulted in a change of accident rates on the I-710. After successfully verifying and validating the authors’ model on the dataset used by Carlin et al. (1992), and Raftery and Akman (1986), the authors analyzed road accidents on the I-710 for 2005 filtered by four (approximately 6 mile) segments and four time periods corresponding to different traffic regimes. The authors generated the probability distribution of the difference between accident rate parameters and built 95% High Density Intervals. Results indicate that there was no significant change in accident rate in 2005 following the implementation of PierPASS. To the authors’ knowledge, this is the first time that a three stage hierarchical Bayesian change point model with MCMC was applied to a transportation problem.