That's because NHTSA studies in 2009 (pdf) and 2011 (pdf) confirmed what many long suspected: Hybrids and electric cars are too quiet for the blind or even the fully sighted to hear them coming. Though the NHTSA found little statistically significant difference in collisions over 35 mph—when wind and tire noise negate the difference in engine noise—at lower speeds, hybrids and electric vehicles are 37 percent more likely to hit walkers and 66 percent more likely to collide with cyclists than traditional gas-powered cars.
NHTSA is tasked with starting the process to develop rules for “minimum” car noise this summer.
If the studies above are valid I guess it is necessary, but alas consider the joy of walking through cities like NYC or SF in the not so distant EV dominated future and hearing only the gentle hum of tire on asphalt. I wonder if in fact, in that quieter atmosphere if EVs don’t already make enough to be heard, its only the din of all the existing gas engines the covers up their softer foot falls.
The BMW i8 Spyder features sound generation, which is cool at first, but I could see it being annoying after a while, and certainly the combined cacophony of scores of EVs with generated sound would be downright irritating.
NHTSA suggests that volume levels below what most gassers produce would be sufficient to warn pedestrians.