Detection of hybrid and quiet vehicles by blind and visually impaired pedestrians

The increased popularity of hybrid electric vehicles has created a growing concern for the safety of blind and visually impaired pedestrians. Accident data published by the National Highway Traffic Safety Administration demonstrates a higher incident rate among hybrid electrics vehicles compared to internal combustion engine vehicles during slow speed movement, like when coming to a stop and leaving/entering a parking spot. The typical lower sound output of hybrid electric vehicles, compared to internal combustion engine vehicles, has been reported as the reason for higher incident rates. Previous studies have focused on the overall sound pressure level of vehicles and the ability for blind pedestrians to detect their approach. Under more controlled conditions and lower ambient sound pressure levels than was achievable in previous research, measurements were made comparing the detection of hybrid electric vehicles, internal combustion engine, and hybrid electric vehicles with added sounds. Forward moving and backward moving vehicle detection tasks confirm that a hybrid electric vehicle is detected by blind pedestrians at a shorter distance and with less time to passing when compared to traditional internal combustion engine vehicles traveling at slow speeds. Adding sound to a hybrid electric vehicle resulted in detections made at a greater distance and with more time to passing the participant location. Five different sounds were tested for hybrid electric vehicles with added sounds. Performance of three of these sounds was statistically significantly better than an identical hybrid electric vehicle with no added sound. Finally, it was found that at detection approaching vehicles had the most acoustic energy above ambient levels in the 1000 and 2000 Hz 1/1-Octave bands at the time of detection.