Evaluating Effect of Two Allowable Permissive Left-Turn Indications

Abstract

NCHRP Report 493 recommended that a flashing yellow arrow (FYA) permissive indication be included in the Manual on Uniform Traffic Control Devices as an alternative option to the circular green (CG). However, as implementation of the FYA permissive indication proceeds, there will be two permissive indications for practitioners to consider at protected–permissive left-turn applications. Using two signal indications that provide drivers with the same message has the potential to increase driver error. Specifically, once drivers are exposed to and understand the meaning of the FYA, it is unclear as to expectancy violations and the likelihood of incorrect interpretation of the CG as a protected left-turn indication. This research employed a multifaceted behavioral experiment, including a dynamic driving simulator experiment and computer-based static evaluations, to quantify any change in driver comprehension of CG indications resulting from the FYA permissive indication. In the simulator, comprehension of the CG permissive indication following exposure to the FYA permissive indication did not differ significantly from driver comprehension of the CG before exposure to the FYA. In a follow-up static evaluation, drivers exposed to the FYA permissive indication were actually more likely to give yield (correct) responses to the CG permissive indication. In a separate independent static evaluation of 100 drivers, the breakdown of responses did not differ statistically from responses collected before and after exposure to the FYA. Results provide little evidence to suggest that the FYA implementation will affect driver comprehension of the CG.