Sound Advice
Volume 12, Issue 2, 2009
Honk If You Think It's Too Quiet!
 The Noise Pollution Clearinghouse published an interesting article in its Spring newsletter, regarding the noise levels created by hybrid cars. Shortly after hybrid and electric cars hit the streets, an odd phenomenon occurred in that people complained about how quiet those cars are. Don't they present a bigger danger to the public because they can't be heard as readily as gas and diesel powered automobiles? Aren't blind people at greater risk since they'll have less warning of the vehicle's approach? Can the manufacturers of hybrid and electric vehicles be made to add some kind of noise device to make the cars safer? A bill in the US House of Representatives, HR 5734, calls for the establishment of a pedestrian alert vehicle safety standard. I think the vehicles are already equipped with a suitable warning device: the horn.
The Clearinghouse article, A Noisy Hybrid?, puts forth the argument that hybrids present no greater risk than other cars. The reasoning is that traffic noise as a whole masks (that is, covers up or disguises) the sound of individual cars anyway, and the noise level in many urban areas is such that any pedestrian, blind or sighted, would have difficulty picking out the sound of a specific vehicle that poses an imminent danger. The primary noise sources from any vehicle are the engine and the tires. The article states that above 45 mph, hybrid and gas-powered vehicle noise levels are the same anyway, since the dominant noise source at that speed is tire noise. Because of the high background noise levels, the author claims, adding noise to hybrid and electric cars to make them safer would have the effect of increasing the overall traffic noise, causing even greater masking effect of individual vehicles and effectively making the situation worse.
A situation that this article fails to address, however, is that of the audibility of vehicles in an average quiet suburban neighborhood housing tract not adjacent to a major arterial or freeway. In my quiet neighborhood, the sound of an approaching gas-powered car is distinctly audible, whereas a hybrid or electric car cruising the streets at or less than a lawful 25 mph is extremely difficult to hear. In these neighborhoods, such vehicles definitely pose a greater threat to the sight-impaired or to children playing in the street.
As usual, it's a balancing act between the needs of the community as a whole and the needs of a small number of individuals more likely to be exposed to a greater risk. Perhaps the answer lies in the education of the drivers of hybrids and electrics. Since the choice of an extremely quiet vehicle is theirs, it may be appropriate for them to undergo specialized training. That training could educate the drivers about the unique acoustic qualities of their cars and the need to be extra vigilant when driving slowly in quiet residential and commercial neighborhoods. Then all that would be necessary to sound the alert is the expedient use of the car horn on an as-needed basis. In other words: honk if you think it's too quiet!
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