A study was conducted to assess the differences in operations and driver behavior when driverswere confronted with three different signal displays for the permissive interval of aprotected/permissive left-turn (PPLT) phase. A comparative two-phased approach, based on fieldobservations and video recordings of driver behavior was used to conduct this research. ThePhase I research examined driver behavior at six intersection approaches in Peoria, Illinoisoperating with different permissive left-turn displays: circular green (CG), flashing yellow arrow(FYA) and flashing red arrow (FRA). Historically the CG indication was the predominantindication used for the left-turn permissive indication in Peoria, until 2010 when FYAs wereinstalled throughout the city. The FRA is operated at two adjacent intersections in Peoria andwere installed as site-specific countermeasures. The Phase I research found that the FYA had thehighest proportion of drivers’ safe and efficient actions combined as compared to the CG andFRA displays. In Phase II, a comparative analysis of four intersection approaches was conductedto determine the impacts on driver understanding of the permissive left-turn circular greendisplay in two geographic areas: one in Peoria that currently uses multiple permissive left-turnsignal indications for the PPLT phase (CG, FYA, and FRA) and the second in Bloomington,Illinois that only uses the CG indication. The Phase II research found that there were nodifferences in driver understanding of the CG permissive left-turn display at the studyapproaches between the two cities, based on the observed safe and efficient driver actions.
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