Are hybrid cars too quiet?

Abstract

The increase in availability of alternative fuel vehicles has elicited concerns for pedestrians who might not hear the approach of these quieter cars. Three experiments tested the relative audibility of hybrid vehicles (in their electric mode) and internal combustion engine (ICE) cars. Binaural recordings were made of the cars approaching from either the right or left, at 5 mph. Subjects were asked to listen to these recordings over headphones and press one of two buttons indicating from which direction the car approached. Subjects’ accuracies and reaction times were measured. The first experiment revealed that (sighted) subjects were able to determine the approach direction of the ICE cars substantially sooner than the hybrid cars. A second experiment added the natural background sounds of idling engines to the stimuli. The addition of background sound disproportionately hindered perception of the hybrid cars, so that they could not be localized until very close. A final experiment testing both sets of stimuli with blind subjects revealed the same pattern of results. Implications of these results for pedestrian safety will be discussed. [Work supported by a grant from the National Federation for the Blind.]

Detectability study of warning signals in urban background noises: A first step for designing the sound of electric vehicles

“…Are hybrid cars too quiet ? This question, posed by Robart & Rosenblum some years ago [1], can define quite well the general framework of the present study. In fact, the main specificity of Quiet Vehicles (QV) -either electric (EV) or hybrid in electric mode (HEV) -is that they are rather completely zero emission with regards to sound, at least in a certain range of use.…”

Auditory Perception of Motor Vehicle Travel Paths

“…Detection of approaching vehicles. Robart and Rosenblum (2009) recorded hybrid (electric mode) and gasoline vehicles approaching at 8 km/h from the left or right. Listening through headphones, participants reported the approach direction.…”

“…Research has also been conducted on sound sources moving on straight paths, including direct approach toward the listener (Bach, Neuhoff, Perrig, & Seifritz, 2009;Rosenblum, Wuestefeld, & Saldana, 1993) and transverse or "miss" paths (Kaczmarek, 2005;Lutfi & Wang, 1999). A distinction between the underlying cues for changing direction or distance of a sound source is that direction is cued primarily by interaural differences, whereas distance is cued by information available at either ear.…”

Vehicle Motion Alarms: Necessity, Noise Pollution, or Both?

“…Although some locations now have signals indicating walk cycles,18 in many locations blind people still cross the street by listening for traffic, explains Deborah Kent Stein of the National Federation of the Blind (NFB). Lawrence Rosenblum, a psychology professor at the University of California, Riverside, performed audibility experiments on HEVs at the request of the NFB 19. “When hybrids are moving slowly, five miles per hour, they are substantially less audible, and depending on background context, we feel dangerously so,” Rosenblum says.…”