## 4 Discussion  
On the one hand, pedestrian crossing decision-making appears to be based mainly on the readily assessable visual information of an approaching vehicle, specifically its speed and distance [18]; on the other hand, auditory cues can play an important role in both detecting and improving locating of approaching vehicles [11; 12]. The increasing presence of hybrid and electric vehicles raises important questions about the impact of auditory cues on pedestrian safety, especially in situations of conflict between pedestrians and vehicles, such as in cases of crossing the road when a vehicle is approaching [7; 13; 14; 16]. The purpose of this study was to contribute to this ongoing discussion by assessing the influence of the type of sound emitted by a vehicle and the auditory cues on pedestrian crossing decision-making, without neglecting the role of the vehicle speed and distance, as well as its movement pattern. Three types of stimuli were presented to the participants, corresponding to the approach of a vehicle with different movement characteristics: a vehicle emitting the sound of an electric car, a vehicle emitting the sound of a gasoline combustion car, and a vehicle with no audio component. The results show that, contrary to the hypothesis of this study, the type of emitted sound had a negligible influence on the number of times the participants decided to cross the road. On the other hand, the movement pattern of the approaching vehicle seemed to play a more relevant role. In general, participants only chose to cross when the vehicle displayed signs of slowing down. For a vehicle starting distance of 30 m and a constant speed of 30 km/h, most participants assumed that it was not safe to cross the road. The analysis of the number of crossings as a function of response times confirmed this conclusion. At constant speed stimuli, the very few crossings occurred at an early  
Figure 8: Mean speed of the vehicle at the moment of the participants’ response and respective mean standard error as a function of auditory condition per vehicle speed pattern. stage of the stimulus presentation, while, in stimuli where the vehicle speed decreased, the participants waited for the approaching vehicle to reach lower speeds in order to communicate their decision to cross. The gasoline combustion vehicle seemed to lead to faster crossing decisions, particularly in the stop condition. However, this also meant that participants crossed when the speed was still relatively high, which, counter-intuitively, ended up resulting in lower TTP values at the time of crossing decision. The shorter response times for gasoline could, at first view, indicate a better trajectory estimation for louder vehicles. However, a difference was not found between the electric and no sound conditions. In addition, when analyzing vehicle distances and speeds at the time which the responses were given, it is apparent that the participants' decision was based primarily on the vehicle distance, which was specific for each vehicle speed pattern. For each of the three different auditory conditions, participants clicked on the computer mouse when the vehicle was always at the same distance. That distance selected by the participants was greater for higher approaching speed conditions. Expectably, the similarity in distances should have been accompanied by similarities in vehicle speed, if the vehicle speed and its evolution over time were exactly the same in the three types of auditory condition. In such cases, no difference would have been observed in the TTP values and response times when the three auditory conditions were compared. However, differences in speed of about 1.7 km/h existed between conditions, resulting from the manual driving variability during the CPB and movement trajectories acquisition sessions. This difference contributes to explain the slightly lower TTP values for gasoline vehicle in the stop condition.