Prohibiting left-turn movements at mid-block unsignalized driveways: Simulation analysis

In recent years, there has been major interest in "access management" as a new response to the ubiquitous traffic congestion problem. Among the different access management strategies is the idea of prohibiting left-turn movements at unsignalized driveways. In this study, the Corridor Simulation traffic simulation model was used to evaluate the operational impacts of different left-turn treatments at mid-block intersections on different classes of roadway facilities. The study also examined the impact of varying the arterial and driveway volume on the effectiveness of restricting direct left turns and providing alternative movements. Three different alternatives were considered for left-turn treatments at mid-block unsignalized intersections: (1) no restriction of direct left turns from or to driveways; (2) no direct left turns in or out of driveways and diverted traffic makes a U-turn at the next intersections; and (3) no direct left turns in or out of driveways and diverted traffic makes a U-turn at mid-block. Two additional cases were also evaluated: a jug handle design, and no direct left turns in or out of all-but-one driveways (concentrated left turn). The results show very little operational difference between the no restrictions on direct left turns alternative versus the restrictions with the U-turn alternative movements from site to site. The jughandle design appeared to be a superior alternative for accommodating left-turn deterred traffic for multilane divided and undivided sites compared to mid-block or intersection U-turns. In addition, it is shown that the concentrated left turn appears to be an excellent solution for improving traffic flow conditions.