Sounds For Silent EVs: Solving a Problem That May Not Exist

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A new study concludes that Prius repairs cost 8.4 percent more than repairs on non-hybrid economy cars.

A new study concludes that Prius repairs cost 8.4 percent more than repairs on non-hybrid economy cars.

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It's a wonderful TV news flash: Blind people in peril from killer electric cars! News at 11. The fear is that electric vehicles are so silent that blind people can't hear them coming, so new draft safety regulations may now require electric vehicles to emit sounds.

There's just one problem: Accident data from the National Highway Traffic Safety Administration show no increase in deaths for blind people in pedestrian accidents during the 10 years that hybrid-electric vehicles have been sold.

Full hybrids, including the definitive 2010 Toyota Prius, are a proxy for EVs because they can operate in full electric mode at low speeds. With the gasoline engine off, the only sounds they emit are tire noise plus a slight whine from the electric motor.

Pedestrian Fatalities, 1994-2008, from NHTSA Fatality Reporting System data

Pedestrian Fatalities, 1994-2008, from NHTSA Fatality Reporting System data

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Early data showed problem

Preliminary data seemed to show that hybrids were more likely to be involved in pedestrian crashes or hit cyclists. An NHTSA report issued last November aggregated accident reports from certain states.

It concluded that hybrids like the Toyota Prius were involved in pedestrian crashes at a rate of 0.9 percent, half again as high as the 0.6 percent rate for gasoline vehicles. Hybrids were also twice as likely to have hit cyclists, at a rate of 0.6 percent versus 0.3 percent.

To its credit, that report noted its own methodological weaknesses. Only 12 states record vehicle identification numbers (VINs) of cars involved in accidents, allowing hybrids to be distinguished from gasoline cars. And only accident data from 2000 or later was used, cutting the size of the sample set.

A more comprehensive look

But now EV enthusiast Mark Larsen (he's also an Emeritus Professor of Spanish at Utah State University) has analyzed some additional data. He used 1994-2008 figures from the Fatality Reporting System maintained by the NHTSA.

If silent hybrid vehicles posed a threat to pedestrians, he reasoned, then the number of pedestrian deaths should have risen since 2000, when the first hybrids were sold. There are now roughly 1 million hybrid-electric vehicles among the 300 million on U.S. roads.

But in fact, despite increasing numbers of hybrids on the roads, the rate of pedestrian fatalities has in fact fallen over that same period.

Total Traffic Fatalities, 1994-2008, from NHTSA Fatality Reporting System data

Total Traffic Fatalities, 1994-2008, from NHTSA Fatality Reporting System data

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Next up, please: Injuries

We like Larsen's analysis, but we would observe that it has two problems. First, it doesn't factor in Vehicle Miles Traveled, which is  correlated with a fall in accident deaths. The rate of deaths per VMT has declined for decades, as cars come with more crash safety equipment.

Second, Larsen really only addresses half the issue. Fatalities from accidents are one data point, but injuries would be another--and are far more common than deaths.

Since hybrids and electric vehicles are at their quietest at low speeds--below 15 miles per hour, say--we'd suggest that if there is a danger from silent vehicles, it would be reflected not in deaths but in injuries.

Larsen nods to this by noting that throughout the study period, not a single blind pedestrian was killed by a vehicle traveling at less than 20 miles per hour. His report is silent, however, on non-fatal injuries that may have been suffered by blind pedestrians.

We eagerly await the arrival of someone's analysis of injury data along the same lines as Larsen's fatalities study.


 
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