Auditory Detectability of Hybrid Electric Vehicles by Blind Pedestrians

Hybrid electric vehicles (HEVs) in low-speed operation may introduce a safety issue for pedestrians. This study compares the auditory detectability of HEVs and internal combustion engine vehicles among pedestrians who are legally blind. Independent travelers, with self-reported normal hearing, listened to binaural audio recordings of two HEVs and two internal combustion engine vehicles in three operating conditions and two different ambient sound levels. The operating conditions include approaching at a constant speed (6 mph), backing out at 5 mph, and slowing from 20 to 10 mph (as if to turn right). The ambient sound levels simulated a quiet rural [31.2 dB(A)] environment and a moderately noisy suburban [49.8 dB(A)] environment. Overall, participants took longer to detect HEVs (operated in electric mode). Vehicle type, ambient level, and operating condition had a significant effect on response time. Candidate countermeasures are discussed in terms of types of information provided (direction, rate of speed change), useful range of detection of vehicles by pedestrians, warning time, acceptability, and barriers to implementation.