Guidelines for the use of protected/permissive left-turn signal phasing were developed by collecting and analyzing data on traffic and roadway conditions for protected-only, protected/permissive, and permissive left-turn phasings to identify relationships among these conditions and signal phasings. The following left-turn signal aspects are addressed:(a) traffic volume based on the peak-hour minimum left-turn volume and the product of the peak-hour left-turn and opposing volumes with lower and upper limits,(b) annual left-turn accident experience based on the er itical number and rate,(c) left-turn traffic conflict experience based on the critical number and rate,(d) left-turn delay,(e) site condition,(f) user cost savings for protected/permissive versus protected-only left-turn phasing, and (g) traffic engineering judgment.

Protected/permissive (P/P) left-turn signal phasing is a combination of a protected phase, in which a green arrow indicates a protected turn, and a permissive phase, in which the left-turning vehicles must yield to the opposing traffic during the green indication. The primary intent is to increase the efficiency of traffic flow by permitting left-turning movements through gaps in the opposing traffic at intersections where traffic volumes warrant a separate left-turn phasing. P/P phasing also reduces delay and energy consumption. However, in two research efforts it was found that accidents involving lef t-turning vehicles increased after the installation of P/P signals<!,~). The number of accidents appeared to decrease as drivers became familiar with the signals, and driver understanding of the P/P phasing was identified as an important factor. However, because at some intersections operational and accident problems have not decreased over time, it appears that factors other than unfamiliarity cause problems. Because the guidelines for a separate left-turn signal found in the literature vary considerably, no clear, consistent set of guidelines could be derived from a synthesis. Moreover, the quantitative guide-