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The contents of this report reflect the views of the author(s), who is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Virginia Department of Transportation, the Commonwealth Transportation Board, or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. Any inclusion of manufacturer names, trade names, or trademarks is for identification purposes only and is not to be considered an endorsement.


Addressing Dilemma Zone Issues With Control Solutions
Montasir M. Abbas, Ph.D., P.E., Qichao Wang, Brian J. Higgs, Ph.D., Donia Zaheri Sarabi, Sahar Ghanipoor Machiani, Ph.D., Milos N. Mladenovic, Ph.D., and Shrikant Fulari
Year: 2017
VTRC No.: 17-R14
Abstract: Rural, high-speed signalized intersections are associated with vehicle crashes attributable to problems in dilemma zones (DZs). DZs are areas where at the onset of yellow, some drivers may decide to proceed and some may decide to stop. This disagreement among drivers can lead to rear-end crashes and/or right-angle crashes.

The purpose of this study was to evaluate different DZ protection methods and provide general guidelines with regard to the strengths and weaknesses of each method. Researchers developed general guidelines to assist engineers at the Virginia Department of Transportation in selecting the best DZ-protection method, based on a comparison of the estimates of predicted safety benefits for the different methods for a given set of traffic conditions.

The results of this study indicate that green hold/termination systems and radar-based protection systems are superior to the multi-loop system, with the radar-based system providing the most protection. This is attributed to the capability of the radar-based system to monitor vehicle speeds continuously and act accordingly, whereas the green hold/termination system assumes constant vehicle speeds. The results also indicate that the prevailing multi-detector loop setups perform differently depending on traffic volume.

The study recommends that the software developed in this study (DZ-Pro) be used to optimize the configuration of the detectors for the existing traffic volume. A before-and-after comparison of the frequency of red-light running indicated a significant reduction in red-light running (up to 80% reduction) when the radar-based DZ protection system was activated.