Auditory Perception of Motor Vehicle Travel Paths.

Objective: These experiments address concerns that motor vehicles in electric engine mode are so quiet that they pose a risk to pedestrians, especially those with visual impairments. Background: The "quiet car" issue has focused on hybrid and electric vehicles, although it also applies to internal combustion engine vehicles. Previous research has focused on detectability of vehicles, mostly in quiet settings. Instead, we focused on the functional ability to perceive vehicle motion paths. Method: Participants judged whether simulated vehicles were traveling straight or turning, with emphasis on the impact of background traffic sound. Results: In quiet, listeners made the straight-or-turn judgment soon enough in the vehicle's path to be useful for deciding whether to start crossing the street. This judgment is based largely on sound level cues rather than the spatial direction of the vehicle. With even moderate background traffic sound, the ability to tell straight from turn paths is severely compromised. The signal-to-noise ratio needed for the straight-or-turn judgment is much higher than that needed to detect a vehicle. Conclusion: Although a requirement for a minimum vehicle sound level might enhance detection of vehicles in quiet settings, it is unlikely that this requirement would contribute to pedestrian awareness of vehicle movements in typical traffic settings with many vehicles present. Application: The findings are relevant to deliberations by government agencies and automobile manufacturers about standards for minimum automobile sounds and, more generally, for solutions to pedestrians' needs for information about traffic, especially for pedestrians with sensory impairments.