Behavior of Left-Turning Drivers during Permissive Interval of Protected–Permissive Operation

A study was conducted to assess the differences in operations and driver behavior in response to three signal displays for the permissive interval of a protected–permissive left-turn (PPLT) phase. A comparative two-phased approach based on field observations and video recordings of driver behavior was used to conduct the research. Phase 1 examined driver behavior at six intersection approaches in Peoria, Illinois, that operated with different permissive left-turn displays: circular green (CG), flashing yellow arrow (FYA), and flashing red arrow (FRA). The CG indication had been the predominant indication used for the left-turn permissive indication in Peoria until 2010, when FYAs were installed throughout the city. FRAs are operated at two adjacent intersections in Peoria and were installed as a site-specific countermeasure. The Phase 1 findings showed that the highest proportion of drivers' safe and efficient actions was in response to the FYA as compared with the CG and FRA displays. In Phase 2, a comparative analysis of four intersection approaches was conducted to determine the impact on driver understanding of the permissive left-turn CG display in two geographic areas: one in Peoria, where multiple permissive left-turn signal indications for the PPLT phase (CG, FYA, and FRA) are currently in use, and one in Blooming-ton, Illinois, where only the CG indication is used. The Phase 2 research found, on the basis of observed safe and efficient driver actions, that there were no differences in driver understanding of the CG permissive left-turn display at the study approaches in the two cities.