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Improving Left-Turn Signal Intersection Safety

Posted: Nov 1, 2019

MPC research at the University of Utah will improve understanding of the safety performance related to of different left-turn signal light phase indications. Transportation engineers will use the results to model future crash frequencies and guide selection of left-turn phase indications by site, and strategies by time of day.

The researchers studied crash data and conducted an in-depth analysis of selected individual left-turn crashes. They learned more about how flashing yellow arrows, green arrows, green-light-only signals and other strategies impact safety. Protected left-turn phases at signalized intersections are intended to reduce the frequency of angle collisions that result from conflicts between left-turning vehicles and opposing through and right-turning vehicles. Previous research demonstrated the overall safety effectiveness of protected left-turn phases. However, extent of the safety effects for protected-permissive left-turn phases--particularly with the recent introduction of the flashing yellow arrow indication--has not been clearly established.

Juan C. Medina
University of Utah

Safety Effects of Protected and Protected/Permissive Left-Turn Phases

NDSU Dept 2880P.O. Box 6050Fargo, ND 58108-6050