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Evaluating effect of two allowable permissive left-turn indications

TitleEvaluating effect of two allowable permissive left-turn indications
Publication TypeJournal Article
Year of Publication2007
AuthorsKnodler J.Michael A, Noyce DA, Fisher DL
JournalTransportation Research Record
Start Page53
Date Published01/2007
KeywordsDriving Simulation, Left-Turns, Protected/Permissive Signal Control, Traffic

National Cooperative Highway Research Program (NCHRP) Report 493 recommended that a flashing yellow arrow (FYA) permissive indication be included in the MUTCD 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 PPLT applications. Using two signal indications which 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 incorrectly interpretation of the CG as a protected left turn indication. This research employed a multi-faceted 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 one hundred drivers, the breakdown of responses did not differ statistically from responses collected before and after exposure to the FYA. The results provide little evidence to suggest that the FYA implementation will impact driver comprehension of the CG.