Date of Award

August 2020

Document Type


Degree Name

Doctor of Philosophy (PhD)


Human Factors Psychology

Committee Member

Richard A Tyrrell

Committee Member

Andrew T Duchowski

Committee Member

Patrick J Rosopa

Committee Member

Benjamin R Stephens


Cycling with motor vehicle traffic on roadways is inherently risky, and it is important for bicyclists to make themselves conspicuous to drivers, even during daylight conditions. Two experiments manipulated rear-facing bike lights to determine how best to help drivers become aware of a bicyclist’s presence during the daytime. Experiment 1 incorporated closed-road methods in which participants provided subjective ratings of conspicuity from a test vehicle parked at two different distances as they viewed 16 configurations of bike lights displayed by a stationary test bicyclist pedaling in daylight. The results indicated that increasing the luminous intensity and number of lights enhanced the relative conspicuity of bicyclists in daylight even as viewing distance increased. Particularly valuable was using ankle-mounted lights that highlighted the pedaling movement of the bicyclist. In Experiment 2, participants wore a head-mounted eye tracker and searched for bicyclists as they were driven along an open-road route that included a test bicyclist displaying one of four light configurations. Participants pressed a button when they detected that a bicyclist might be present in or near the roadway and again when they were confident that a bicyclist was present. The results revealed that after participants first glanced at the bicyclist it took a significant amount of time to detect and then to recognize the bicyclist. Further, lights that were mounted to the seat post of the bike or to the seat post and the heels of the rider’s shoes provided the greatest conspicuity advantage in terms of the distances from which participants recognized the bicyclist. These experiments offer useful insights into the optimal light intensities and placement options for bicyclists to use in order to enhance their conspicuity during the daytime.



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