Abstract
The results of a comprehensive study on protected and permissive left-turn (PPLT) operations showed that the flashing yellow arrow (FYA) indication was an acceptable and recommended application for permissive left turns. As documented in NCHRP Report 493, an FYA permissive indication was recommended for implementation in the FHWA Manual on Uniform Traffic Control Devices for Streets and Highways (MUTCD). Research findings suggested that the FYA be implemented in an exclusive four-section vertical signal display centered over the left-turn lane, which differs from the most common application of PPLT signal displays. Many traffic engineers currently use a five-section clustered-arrangement shared signal head to meet MUTCD requirements of two signal heads per major approach. FYA implementation in the five-section display would require an interim retrofit requiring the FYA to be displayed simultaneously with the through-movement circular green (CG), circular yellow, or circular red indication. This research evaluated driver comprehension of the retrofit display and the resulting simultaneous indications by using a dynamic driving simulator and computer-based static experiments. A comparison of seven permissive left-turn scenarios featuring the CG or FYA permissive indications, or both, was completed. In total, 264 drivers evaluated 3,457 permissive left-turn scenarios. Results showed that simultaneous indications in the retrofit display did not affect the drivers’ understanding of the permissive indications. The drivers demonstrated an understanding of the yield requirement with simultaneous indications (with a 65% to 89% correct responses), providing evidence to suggest that the simultaneous indications would be suitable as an interim display to ease FYA implementation.
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