Cross-cultural study on feasible sound levels of possible warning sounds for quiet vehicles

Electric and hybrid electric vehicles (EV/HEV) have the advantage of being more environmentally friendly and quieter than internal combustion engine vehicles. However, reduced noise can also lead to potentially dangerous situations for pedestrians when an oncoming vehicle is inaudible due to background noise (e.g. Kerber and Fastl, internoise 2007). The installation of devices that produce warning sounds in vehicles to alert pedestrians is being considered in various countries. Because this is a global topic, it is of vital interest to determine whether there exist cross-cultural differences. Pilot studies on this topic were performed in Japan (Yamauchi et al., internoise 2010) and, with improved input devices and test procedure, in Germany (Menzel et al., DAGA 2011). The level of three possible warning sounds (engine noise, car horn, and band-pass noise) were adjusted in presence of four different urban background sounds (busy street, residential area, heavy traffic, and shopping area) in laboratory environments. In the first part of the experiments, subjects were asked to adjust the level of the warning sounds so that they were clearly audible and could be reliably detected in the background noise. In the second part the goal was to adjust the level so that the warning sounds were just audible. The results of the adjustments showed no significant difference between the two subjects groups. The results were discussed in view of inter-individual and intraindividual differences. Moreover, the results were compared to current recommendations for sound levels of warning sounds in quiet vehicles.