Microscopic Simulation Model of Traffic Operations at Intersections in Malfunction Flash Mode

From time to time, intersection signal hardware malfunctions. In many instances, such a malfunction results in the intersection falling into a flashing operation. While in this mode, the signal indications presented to motorists may be red–red (R-R) flash (i.e., flashing red indications presented to all movements) or yellow–red flash (Y-R) (i.e., flashing yellow indications to the mainline movement and flashing red to all other movements). Transportation agencies must select one of these flash modes for intersection malfunction flash events. To help agencies develop flash mode policies, operational comparisons of Y-R and R-R flash are simulated over a range of volume demands at the intersection of two roadways with two lanes each. Driver behavior at the flashing intersection is modeled according to field data collected at more than 40 instances of malfunction flash. Results indicate that the common assumption that Y-R malfunction flash keeps the mainline moving is often incorrect. Under conditions of low side street volume, this assumption may hold true; however, as major and minor street volumes increase, intersection operation increasingly mirrors that of an all-way-stop-controlled intersection. The key findings are that both Y-R and R-R flash provide reasonable performance at relatively low major and minor street volumes, and both break down at higher volumes. Only over a limited range of traffic demands will Y-R flash provide a significantly better operational performance than will R-R flash.