Deployment of a dilemma zone protection system reduced the maximum length of the dilemma zone by 30 percent at a rural intersection in Maryland.

Improved dilemma zone protection system deployed at two rural intersections in Maryland.

Date Posted

Intelligent Dilemma Zone Protection System at High-Speed Intersections

Summary Information

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.


The maximum length of the dilemma zone was reduced by 960 to 670 feet (vehicles traveling at 75 mi/h), a 30 percent reduction, at the intersection of US 40 and Western Maryland Parkway. The total length of dilemma zones weighted by traffic volume in each speed bin (increments of 5 mi/h from 25 mi/h to 75 mi/h), a 40 percent reduction, from 73 feet to 44 feet. Similar reductions were noted at the intersection of MD 213 and Williams/Locust Point Road.

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