In this study, exclusive left-turn phasing was replaced with permissive left-turn phasing at four trial intersections. Delay and accident studies were done before and after the trial installations. Also, a questionnaire was issued to determine public opinion concerning the signals.

The use of permissive-turn phasing resulted in a 50-percent reduction in left-turn delay and a 24-percent reduction in total delay compared to exclusive phasing. The permissive left-turn phasing did result in an increase in left-turn accidents. Other accident types, such as rear-end accidents, did not change. The number of left-turn accidents decreased as drivers became more familiar with the signals. Questionnaire responses showed that over 90 percent of drivers were in favor of this type of signal. An economic analysis showed that all but one of the locations had benefit-cost ratios much higher than one when a 1-year "after" period was considered. All locations had benefit-cost ratios greater than one when an additional 6 months of accident data were taken into account.

The reductions in delay are encouraging toward additional but discriminating use of permissive left-turn phasing; and, indeed, the increased accident potential limits its use to intersections where an accident problem will not be created.

Report Date


Report Number

No. 519

Digital Object Identifier



The contents of this report reflect the views of the author 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 Bureau of Highways, The report does not represent a standard, specification, or regulation.