In Germany, electric bicycles (pedelecs) have become highly popular over the past few years. Reasons for that are their potential to reach higher speeds and the reduction of cycling effort. While these are desirable effects, safety concerns have been raised. Pedelecs are, with regard to their design, hardly distinguishable from conventional bicycles. It has been argued that this could result in other road users misjudging the approach of an oncoming pedelec (e.g. at intersections) and subsequent unsafe behaviour, e.g. choosing rather small time gaps for crossing in front of pedelec riders. Therefore, the goal of this study was to conduct a series of experiments investigating road users’ time-to-arrival estimations (TTA; the estimation of time gaps between the road user and other vehicles) and their gap acceptance behaviour (the gap a road user selects in front of or between other vehicles for turning or crossing) in relation to approaching two-wheelers, especially pedelecs and conventional bicycles. Three experiments were conducted to investigate the influence of two-wheelers’ approach speed, bicycle/vehicle type (conventional bicycle, S-pedelec, scooter), road gradient, observer perspective, observer age, cyclist age, and pedalling frequency on TTA estimation and/or gap acceptance. A fourth experiment investigated the impact of measures to enhance the visibility of cyclists on TTA estimation. An intersection scenario was implemented either in a realistic setting on a test track (Experiment 1) or in a laboratory using video material (Experiments 2 to 4). On the test track, participants were seated in a real car. They observed an approaching cyclist and were instructed to depress a foot pedal to indicate the smallest acceptable gap to turn in front of the bicycle rider (gap acceptance). In the laboratory studies, participants were asked to indicate the smallest acceptable gap, too, but provided their judgements on the basis of videos of approaching cyclists. For TTA estimations, participants watched short videos of approaching two-wheelers. Before the rider reached the position of the participant, the videos were masked, and the participants were required to press a button to indicate the moment they believed the rider would have reached a predefined position (TTA estimation, Experiment 2 to 4 only). In all four experiments, a higher approach speed of the two wheeler lead to higher TTA estimates and smaller accepted gaps in comparison to a lower approach speed. That means participants’ turning decisions tended to be riskier for higher speeds. In addition, there were differences in gap acceptance and TTA estimation between the two bicycle types. Participants selected smaller gaps for the S-pedelec compared to the bicycle. Likewise, TTA estimations for the S-pedelec were higher, i.e. participants judged the time remaining until the S-pedelec reached the observers’ position as longer compared to the bicycle, resulting in riskier turning behaviour. For the scooter, we found larger accepted gaps and smaller TTA estimations in comparison to the two bicycle types. This suggests a somewhat safer turning/crossing behaviour around scooters compared to bicycles. Furthermore, cyclists’ age influenced TTA estimations, with an older cyclist being judged as arriving earlier at the observers’ position than a younger cyclist. In addition, the participants chose smaller gaps and provided higher TTA estimations for a lower pedalling frequency in comparison to the higher one. The age of the participants affected only TTA estimation, not gap acceptance behaviour. Throughout the experiments, older participants judged TTA as being smaller compared to the younger participants. The measures for enhancing the visibility of the cyclists had no influence on TTA estimation. The results demonstrate that the higher speed of pedelecs together with their similarity to conventional bicycles could indeed result in road safety problems. Simple measures that 7 mainly aim at increasing cyclist visibility do not seem to be suitable to change gap acceptance and speed judgement of pedelecs. The results indicate that observers base their speed judgements and turning/crossing decisions on their experience with conventional bicycles. Therefore it may be more appropriate to develop a unique pedelec design to clearly distinguish it from a conventional bicycle. In the future, it might be that with even more pedelecs on the road other road users will adapt and the difference between pedelecs and bicycles in speed judgments and turning / crossing decisions will disappear. At this point, however, this is mere speculation. (Author/publisher)
Samenvatting