United States Department of Transportation
i
Research on minimum sound specifications for hybrid and electric vehicles
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2012-06-30
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[PDF-3.56 MB]
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Abstract:This report documents research by the National Highway Traffic Safety Administration (NHTSA) to identify ways
to develop sound specifications for electric and hybrid vehicles. The research was conducted to support activities
related to the implementation of the Pedestrian Safety Enhancement Act of2010. The Pedestrian Safety
Enhancement Act (PSEA) requires NHTSA to conduct a rulemaking to establish a Federal Motor Vehicle Safety
Standard (FMVSS) requiring an alert sound for pedestrians to be emitted by all types of motor vehicles that are
electric or hybrid (EVs and HVs). The goal is to establish performance requirements for an alert sound that allows
blind and other pedestrians to reasonably detect a nearby EV or HV. The alert sound must not require activation by
the driver or the pedestrian, and must allow pedestrians to reasonably detect an EV or HV in critical operating
scenarios such as, but not limited to, constant speed, accelerating, or decelerating. Sound specifications would
include criteria for sounds to be detectable and recognizable as the sound of a motor vehicle in operation. Two
concepts to identify potential detectability specifications for alert sounds are explored: (a) minimum sound levels
based on psychoacoustic modeling and detection distances and (b) minimum sound levels based on the sound of
internal combustion engine (ICE) vehicles. Potential detectability specifications are discussed in terms offrequency
range and minimum sound level for selected one-third octave bands. Also considered is the relative proportion of
acoustical energy emitted from a vehicle as a function of direction (directivity). Recognition includes two aspects:
recognition that the sound is emanating from a vehicle and recognition of the type of operation that the vehicle is
conducting. Potential specifications to aid in recognition are discussed in terms of broadband noise and tones (toneto-
noise ratio) and ways to denote changes in vehicle speed (pitch-shifting as a function of vehicle speed).
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