From time to time, traffic signal hardware may experience a malfunction, which automatically places the intersection into flashing operation. While in flash, the signal indications that may be presented to the motorist consist of red–red flash (i.e., flashing red indications presented to all movements) or yellow–red flash (i.e., flashing yellow indications presented to the main-line movement and flashing red to all other movements). Transportation agencies must select one of these two flash modes for intersection malfunction flash events. This paper summarizes current malfunction flash policies and practice. The paper includes a review of state department of transportation policies and guidance related to malfunction flash and the results of a survey of state and local agency officials responsible for traffic signals. No general guidance was found to inform uniformity in flash mode selection. The choice between yellow–red and red–red flash is made on an agency-by-agency basis. Of the signal agencies surveyed, widespread differences were identified in the causes of malfunction flash, flash mode selection policies, notification methods, and maintenance procedures. This study highlights the need for the development of consistent flash mode policies at the national and state levels.
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