Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)



Committee Chair/Advisor

Richard Tyrrell

Committee Member

Benjamin Stephens

Committee Member

Patrick Rosopa

Committee Member

Dawn Sarno


The incidence of pedestrian fatalities has increased dramatically, and insufficient conspicuity at night has been identified as a significant problem. Placing retroreflective markings on a pedestrians’ extremities increases pedestrian conspicuity to drivers at night by capitalizing on our perceptual sensitivity to biological motion (biomotion). This study sought to determine whether biomotion also affects drivers’ ability to judge when they will arrive at pedestrian’s location. Here, 126 participants viewed prerecorded 25-second videos of a nighttime approach towards a walking pedestrian. The pedestrian wore one of five clothing configurations while walking from one of three approach angles. Prior to the vehicle reaching the pedestrian, the videos ended with a mask of one of three durations. Participants estimated the time-to-collision (TTC) between the vehicle and pedestrian by pressing a button at the moment they estimated that the vehicle would reach the pedestrian. Participants generally underestimated TTC, especially when the mask was longer. Retroreflective markings placed on the pedestrian’s extremities induced earlier TTC responses when mask duration was long but led to more accurate responses when the mask duration was shorter. Further, participants had less variable responses when the pedestrian’s extremities were highlighted. This study provides valuable information on factors that influence drivers’ perceptual ability to localize pedestrians at night and reveals that highlighting biomotion information affects drivers’ perceptual localization of pedestrians at night.



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