The two-way left-turn lane (TWLTL) is commonly used to solve safety and operational problems on four-lane undivided roadways that result from conflicts between through-traffic and drivers making mid-block left turns. Numerous studies of the safety effects of TWLTL medians have been conducted, but studies of their operational effects have been limited. Consequently, attempts to develop guidelines for the use of the TWLTL have focused on safety benefits and have not adequately accounted for the operational savings it provides. In this study, computer simulation was used to determine the operational effects of TWLTL medians on urban four-lane roadways. Multiple regression analyses of the results of the simulation runs were conducted to determine the relationships between the operational effects of TWLTL medians and prevailing roadway and traffic conditions. Regression equations were developed for predicting the reduction in stops and delay provided by TWLTL medians. This paper includes a description of the simulation model as well as the procedures, findings, and conclusions of the study.
Abstract