A simulation study of left turning movement at an unsignalized intersection

Abstract

The 1985 Highway Capacity Manual does not provide the methodology for analytical values of the delay at unsignalized intersections. In order to find this delay value, a simulation model is developed. It simulates the judgement of the driver in the left turning lane by checking whether there are vehicles in the potential danger zones. This is similar to finding appropriate critical gaps between successive vehicles in the opposing through lane. The critical point for the driver to make judgement is at the PNR (Point of No Return). The driver will: (1) move on to cross the opposing through lane or (2) brake and eventually come to a full stop at a safe spot, then looking for appropriate gap to cross, both under the condition if the driver has a clear view; or (3) decelerate and reassess the safety if he has the view to the danger zone blocked by the opposing left turning vehicles. The model was to test different combinations of (1) vehicle speeds, (2) average interarrival times, and (3) allowable gaps (a description of driver types) as sensitivity variables. The results generally proved to be reasonable.