Evaluation of traffic signal displays for protected permissive left-turn control using driving simulator technology

The objective of this research was to determine the safety and effectiveness of selected protected/permissive left-turn (PPLT) signal displays through driver comprehension evaluations. Driver evaluations were conducted using full-scale, fixed-base, fully-interactive driving simulators located at the University of Massachusetts and the Texas Transportation Institute. The PPLT displays were also evaluated in a static environment to provide comparison data. The 12 experimental PPLT signal displays evaluated differed in permissive indication, arrangement, location, and through movement indication. Each PPLT signal display included only the circular green ball and/or flashing yellow arrow permissive indications. Driver comprehension was determined from the distribution of correct and incorrect responses. Findings from the driving simulator study showed a high level of comprehension (91%) with no variation between PPLT displays. The lack of significant differences in driver comprehension is itself a significant finding, indicating the flashing yellow arrow is an alternative to the circular green ball permissive indication.