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

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.