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Journal of Safety Research

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Objective: The objective of this experiment was to identify whether drivers comprehended traffic signals differently when turning left at signalized intersections where traffic signals were in “flashing mode” operation. Method:Multivariate multiple response analysis of variance models were used to analyze the simultaneous effects of displayed color combination, age, and geographical location on signal message interpretation. Data were gathered in a laboratory environment. Results: Left-turn and through-signal color combination had a significant effect on subject comprehension. Comprehension was found to be lowest for displays flashing red only, followed by displays flashing red on the left-turn, and yellow on the through-signal, with best comprehended displays flashing yellow only. No overall significant age effects were identified, with one minor exception. No geographical region effects were identified. Signal section arrangement and the use of an arrow or circular illuminated lens had no significant effect on comprehension. Discussion: Traffic signal displays in “flashing mode” operation were previously identified as the least well-comprehended displays for drivers turning left. The present effort identified that this is mainly due to displays flashing red indications on the through-signal. Comprehension of displays flashing yellow indications on the through-signal is comparable to that of permitted left-turn indications. Impact on the Industry: There is a need to develop alternatives for signal displays flashing red indications on the through-signal because a large percentage of drivers facing such indications mistakenly think they have the right-of-way when, in fact, they do not. However, use of such displays on minor streets intersecting major streets cannot currently be avoided when signals are placed in flashing operation. Practitioners using flashing signal operations need not be concerned about signal message comprehension differences among age groups. They can use any among the analyzed alternative signals that convey a given message without impacting signal message comprehension.


Accepted version. Journal of Safety Research, Vol. 32, No. 1 (March 2001): 85-106. DOI. © 2001 Elsevier B.V. Used with permission.

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