Center for Transportation Studies, University of Minnesota
The objective of this project was to develop guidelines for time-of-day use of permitted left-turn phasing,
which can then be implemented using flashing yellow arrows (FYA). This required determining how the risk
for left-turn crashes varied as traffic-flow conditions varied during the course of a representative day. This
was accomplished by developing statistical models, which expressed the risk of occurrence of a left-turn
crash during a given hour as a function of the left-turn demand, the opposing traffic volume, and a
classification of the approach with respect to the opposing traffic speed limit, the type of left-turn protection,
and whether or not opposing left-turn traffic could obstruct sight distance. The models were embedded in a
spreadsheet tool which will allow operations personnel to enter, for a candidate intersection approach,
existing turning movement counts, and a classification of the approach with respect to speed limit, turn
protection, and sight distance issues and receive a prediction of how the risk of left-turn crash occurrence
varies throughout the day, relative to a user-specified reference condition.
Davis, Gary A.; Hourdos, John; Moshtagh, Vahid.
Development of Guidelines for Permitted Left-Turn Phasing Using Flashing Yellow Arrows..
Center for Transportation Studies, University of Minnesota.
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