M. Chakraborty, S. Stapleton, M. Ghamami, T. Gates
Tolling has been recognized as one of the effective ways to reduce traffic congestion. There are three types of tolling systems currently in place, namely, Traditional Toll Plaza, Hybrid Toll Plaza, and All-Electronic-Toll-Collection (AETC) system that includes Open Road Tolling (ORT). More recently, traditional or hybrid toll facilities are increasingly being transitioned to AETCs. The upgrade from the toll plazas to the AETC system has demonstrated operational and environmental benefits. However, little is known about the safety impacts of these new tolling systems. Currently, Texas ranks second in the nation in terms of the length of toll road network. As a case study from Texas, this research determines the safety impacts of the conversion of hybrid plazas to ORT on SH Loop 1 in Austin, Texas. Two different Bayesian approaches, namely Empirical Bayes and Full Bayes methods were utilized in this analysis, using crash data from 2010 to 2015, since the conversions on SH Loop 1 took place in January 2013. The Empirical Bayes also included the development of Safety Performance Functions separately for different severities of crashes. The results from both the analytical methods reveal that an upgrade to the AETC system on SH Loop 1 considerably reduced the total, as well as fatal and injury, and property damage only crashes. Higher crash reduction was observed for the total, and fatal and injury crashes compared to the property damage only crashes. While the crash reduction estimates compare favorably between the two analytical methods, higher estimates for fatal and injury, and property damage only crashes are determined by Full Bayes approach. Overall, this case study provides more evidence to the crash reduction potential of the toll design conversions from hybrid plazas to AETC system using open road tolling and presents a generic understanding of the safety impacts of AETC system.
Keywords: All-Electronic-Toll-Collection (AETC); Open Road Tolling (ORT); empirical bayes; full bayes; safety