Drivers’ actions in an intersection’s dilemma zone, the area where the decision to stop at a yellow light or continue through it is not clear-cut, can lead to side-angle and rear-end crashes. In Maryland, researchers developed an intelligent dilemma zone protection system (DZPS) to reducing these crashes by anticipating drivers’ decisions and responding.
The DPZS system was deployed at two high-speed rural intersections (US-40 at Western Maryland Parkway in Hagerstown, MD and MD-213 at Williams/Locust Point Road in Elkton, MD) and has three components: (1) two wide-range sensors to track speeds and locations of all vehicles within the identified dilemma zones; (2) software to predict the response of drivers during the yellow phase and to activate the all-red extension function if needed; and (3) a web-based module for engineers/technicians to monitor the system’s performance from a control center. Field evaluations of the deployed DZPS were conducted about one month after the system activation dates, and real-time system monitoring and performance analysis was carried out with respect to the traffic flow characteristics impacts and the all-red extension activations.
More drivers were observed making the conservative decision to "stop" during a yellow phase, compared with the driver decisions observed in the before-deployment period. For example, the percentage of drivers deciding to "pass" through the intersection during yellow phases at speeds of 45 to 55 mi/h and 300 to 400 feet from the stop line, decreased from 50 percent for both intersections in the before-deployment period to 43 percent for the intersection of US-40 and Western Maryland Parkway and 18 percent for the intersection of MD-213 and Williams/Locust Point Rd in the after-deployment period.