Integrated Safety and Operational Analysis of the Access Design of Managed Toll Lanes

Abstract

Managed lanes (MLs) have been implemented as a vital strategy for traffic management and traffic safety improvement. The majority of previous studies involving MLs have adopted a limited scope of examining the effect of MLs segments as a whole, without considering the safety and operational effects of the design of access to the MLs. In the study, several scenarios were tested using microscopic traffic simulation to determine the optimal access design while taking into consideration accessibility levels and weaving lengths. The studied accessibility levels varied from one to three along the studied network. Both safety (i.e., speed standard deviation, time-to-collision, and conflict rate) and operation (i.e., level of service, average speed, average delay) performance measures were included in the analysis. Tobit models were developed for investigating the factors that affect the safety measures. ANOVA and LOS calculations were used to evaluate traffic operation. The results of the safety and operational analysis suggested that one accessibility level is the optimal option in the nine-mile network. A weaving length between 1,000 feet and 1,400 feet per lane change was suggested based on the safety analysis. In addition, from the operation perspective, a weaving length between 1,000 feet and 2,000 feet per lane change was recommended. The results also showed that off-peak periods had better safety and operational performance (e.g., lower conflict rate, less delay) than peak periods. This study has major implications for improving MLs by recommending the optimal accessibility level and weaving length near access zones.