The influence of speed, cyclists’ age, pedaling frequency, and observer age on observers’ time to arrival judgments of approaching bicycles and e-bikes

• The effect of speed, bicycle type and other factors on TTA estimates were examined.
• Older observers provided consistently shorter TTA estimates than younger ones.
• Higher speed resulted in significantly longer TTA estimates.
• Estimates for a conventional bicycle were significantly shorter than for an e-bike.
• Reduced pedalling effort for the e-bike rider can be an explanation for this effect.

Given their potential to reach higher speed levels than conventional bicycles, the growing market share of e-bikes has been the reason for increased concerns regarding road safety. Previous studies have shown a clear relationship between object approach speed and an observers’ judgment of when the object would reach a predefined position (i.e., time to arrival, TTA), with higher speed resulting in longer TTA estimates. Since TTA estimates have been linked to road users’ decisions of whether or not to cross or turn in front of approaching vehicles, the higher potential speeds of e-bikes might result in an increased risk for traffic conflicts. The goal of the two experiments presented in this paper was to examine the influence of speed and a variety of other factors on TTA estimation for conventional bicycles and for e-bikes. In both experiments, participants from two age groups (20–45 years old and 65 years or older) watched video sequences of bicycles approaching at different speeds (15–25 km/h) and were asked to judge the TTA at the moment the video was stopped. The results of both experiments showed that an increase in bicycle approach speed resulted in longer TTA estimates (measured as the proportion of estimated TTA relative to actual TTA) for both bicycle types (ηp2Exp.1 = .489, ηp2Exp.2 = .705). Compared to younger observers, older observers provided shorter estimates throughout (Exp. I: MDiff = 0.35, CI [0.197, 0.509], ηp2 = .332, Exp. II: MDiff = 0.50, CI [.317, 0.682], ηp2 = .420). In Experiment I, TTA estimates for the conventional bicycle were significantly shorter than for the e-bike (MDiff = 0.03, CI [.007, 0.044], ηp2 = .154), as were the estimates for the elder cyclist compared to the younger one (MDiff = 0.05, CI [.025, 0.066], ηp2 = .323). We hypothesized that the cause for this effect might lie in the seemingly reduced pedaling effort for the e-bike as a result of the motor assistance it provides. Experiment II was able to show that a high pedaling frequency indeed resulted in shorter TTA estimates compared to a low one (MDiff = 0.07, CI [0.044, 0.092], ηp2 = .438). Our findings suggest that both the e-bikes’ potential to reach higher speeds and the fact that they reduce the perceived cycling effort increase the risk of TTA misjudgments by other road users.