Cyclist Perception–Reaction Time and Stopping Sight Distance for Unexpected Hazards

Cyclist perception–reaction time and deceleration rate have not been previously measured for unexpected hazards, which is a major knowledge gap for the design of safe bicycle facilities. This research aims to determine the distributions of perception–reaction time, deceleration rate, and stopping sight distance for cyclists in response to an unexpected, fixed object in their path that requires an emergency stop. Cyclist braking was measured in response to both unexpected and expected stimuli to balance risk and representation for a total sample of 302 participants. The 85th percentile perception–reaction time for an unexpected hazard was 0.84 s, substantially shorter than in motor vehicle studies and design guidance, possibly due to heightened vigilance when riding a bicycle. In contrast, the 85th percentile deceleration rate was 0.20g (1.96 m/s2), smaller than some design guidance, possibly due to the risk and complexity of hard braking on a bicycle. Lower self-reported confidence when cycling was associated with shorter perception–reaction time and smaller deceleration rate, suggesting increased vigilance and greater caution when braking. Neither age nor gender were significant predictors of perception–reaction time or deceleration rate, although men had higher approach speeds, which increased their total stopping sight distance. These findings provide evidence-based parameter values for design of safe bicycle facilities considering the performance of a diversity of cyclists.