Novel Cell Transmission Model–Based Simulations of Left-Turn Blockages inside Intersections

Simulation of oversaturated traffic conditions, especially those that involve left-turn blockages, remains a challenge. In oversaturated conditions, left turns at intersections not only are blocked by the oversaturated through traffic in the same direction but can also be blocked by spillback into the intersection from the through traffic in the opposite direction. This research developed and tested a new model, proposed as the conditional cell transmission model (CCTM). This model allows for the possibility of the formation of an additional cell in an intersection to account for any vehicles that may be caught there for some amount of time and incur delay that may potentially cause delay to conflicting movements. The results of experiments demonstrated that (a) the CCTM could accommodate various traffic demands properly and accurately represent left-turn blockages at intersections, (b) the CCTM had the ability to simulate left-turn blockages within an area inside an intersection, and (c) the CCTM uniquely allowed users to input the probability of a conditional cell and the probability of the occurrence of a useful gap to match the behavior of local drivers. The third feature is a unique contribution of the CCTM. Finally, the consistency between Highway Capacity Manual procedures and the CCTM shows that the CCTM is a reliable methodology with which to model traffic flow in oversaturated conditions.