Evaluation of Sounds for Hybrid and Electric Vehicles Operating at Low Speed

Electric vehicles (EV) and hybrid electric vehicles (HEVs), operated at low speeds may reduce auditory cues used by pedestrians to assess the state of nearby traffic creating a safety issue. This field study compares the auditory detectability of numerous synthetic sounds for hybrid and electric vehicles operating at a low speed. The sample includes pedestrians who are sighted and legally blind, independent travelers, with self-reported normal hearing. The test site has the acoustic characteristic of an urban area with a typical ambient noise level of approximately 58-61 dB (A). Dependent variables include proportion of detection and detection distance. Synthetic sounds tested, that resemble those of an internal combustion engine (ICE) vehicle, produce similar detection distances as the actual ICE vehicle tested for a 6 mph constant speed operation. In some instances, synthetic sounds designed according to psychoacoustic principles were detected much sooner than the reference ICE vehicle tested. Synthetic sounds that contain only the fundamental component of combustion noise, but lack the harmonics and other high-frequency characteristics of an actual ICE were relatively ineffective, with their detection distances being only about half of those of an ICE vehicle.