AN EVALUATION OF THE FLASHING YELLOW ARROW PERMISSIVE INDICATION FOR USE IN SIMULTANEOUS INDICATIONS

The recently completed National Cooperative Highway Research Program (NCHRP) Project 354 was a comprehensive, national research study to evaluate operational advantages and safety aspects of various left-turn controls at signalized intersections. After a series of studies that included evaluations of driver-based human factors, driver comprehension, and intersection operations, the NCHRP 3-54 research team concluded that a flashing yellow arrow (FYA) permissive indication provided a viable alternative to the circular green (CG) permissive indication. Therefore the research team recommended the FYA permissive indication be included in the Federal Highway Administration’s (FHWA) Manual on Uniform Traffic Control Devices (MUTCD) as an acceptable and perhaps recommended indication for permissive leftturns. The NCHRP recommendations suggested the FYA be implemented in an exclusive signal display centered over the left-turn lane, which differs from many existing protected-permissive left-turn (PPLT) signal displays currently in use. The most common application of PPLT signal displays is the use of a shared signal head (centered over the lane line between the left-turn lane and adjacent through lane) to meet MUTCD requirements of two signal heads per major approach movement. As a result, the implementation of the FYA in this display would require the FYA be displayed simultaneously with the through movement indication of circular green, circular yellow, or circular red. There was a need to research driver comprehension of the FYA permissive indication when it is used in a simultaneous display. This research evaluated driver comprehension of the resulting simultaneous displays using a dynamic driving simulator experiment, follow-up computer-based static evaluation as well as an independent static evaluation completed in both Amherst, Massachusetts and Madison, Wisconsin. A comparison of seven different permissive left-turn scenarios featuring the CG and/or FYA permissive indications was completed. In total, 264 drivers participated in the research, evaluating 3,457 permissive left-turn scenarios. In the driving simulator, the simultaneous indications in the retrofit display (simultaneous indication display) did not improve nor reduce driver’s understanding of the display. In a follow-up static evaluation, yield responses ranged from a low of 65 percent for the CG permissive indication in a five-section cluster configuration to a high of 89 for the proposed retrofit display. Therefore, there is evidence to suggest that the simultaneous indications in the retrofit display may improve driver’s comprehension of the permissive indication.