Sunday, February 13, 2011

Hybrid Cars: Higher Crash Risk for Pedestrians and Cyclists

Hybrid cars have been touted by many as a way to reduce the environmental impacts of driving and save money at the pump. Many of them boast impressive fuel economy, although there are questions about their life-cycle environmental impacts (the impact of making, using, and disposing of them) given their large batteries.

I'd like to think that hybrids can play a constructive role in a balanced transportation system. However, a report I recently noticed from NHTSA kind of threw a bucket of cold water on that, for now at least.

"This study found that pedestrian and bicyclist crashes involving both HEVs [hybrid electric vehicles] and ICE [internal combustion engine] vehicles commonly occurred on roadways, in zones with low speed limits, during daytime and in clear weather, with higher incidence rates for HEVs when compared to ICE vehicles."

"Similar to pedestrians, in crashes that potentially have occurred at very low speed such as when vehicles are turning, slowing, or stopping, backing up, or entering or leaving a parking space, the incidence rate of bicyclist crashes involving HEVs was significantly higher when compared to ICE vehicles."

"In conclusion, this study found that HEVs have a higher incidence rate of pedestrian and bicyclist crashes than do ICE vehicles in certain vehicle maneuvers."

Source: Hanna, Refaat (2009). "Incidence of Pedestrian and Bicyclist Crashes by Hybrid Electric Passenger Vehicles", page 3.
What's the solution? The Nissan Leaf may be pointing the way with an artificial sound system that alerts other road users to the car's presence. Such systems should be tested for their efficacy (and lack of nuisance) and if found effective should be made mandatory by government regulation for all electric and hybrid cars.

Another point is that it's very difficult to get a handle on the problems caused by cars just by trying to improve the cars themselves. One solution (hybrid drive train) can create another problem (higher pedestrian and cyclist risk). Hence, we shouldn't forget that if we planned our cities well, we wouldn't be so damn dependent on cars in the first place! :)


  1. i suspect hybrid vehicles injure pedestrians and bikers much less severely.

  2. If you have any studies on that, I'd be interested in seeing them.

  3. sure, light cars may be less likely to inflict a severe injury, but hybrids are generally heavier than other cars their size.

    anyway the main issue is sound, or lack thereof. which means we're going to need to start looking and not just listening.

  4. As a bike-rider who enjoys a little one-ear entertainment while she rides, I kind of hate to say it, but earphones are NOT our friend in a world of near-silent motor vehicles.

  5. A law was recently passed which will mandate noisemakers on quiet cars going forward. I'm not in favor of the law, since I'm a noise-sensitive person and prefer to be around quieter cars when I'm walking around neighborhoods.

    I believe the Prius has always made a chirping alarm when it is moving in reverse, so it doesn't make much sense why there would be a higher incidence of reversing crashes -- or it might prove that noisemakers aren't helpful (the car has some rather goofy rear visibility anyway, which would seem the more likely culprit to me). Also, while Toyota hybrids (and those based off the Hybrid Synergy Drive like the Ford Escape) are able to completely disengage and stop the engine to operate silently, Honda hybrids always have the engine running when they are in motion.

    Hybrids which can disengage the engine tend to be just as noisy as regular cars when they're traveling at speeds above 20 or 25 mph. They're only really "silent" when they're going below those speeds. It's important to note that crashes at slower speeds are much less injurious than those at higher speeds. I think the chance of death in a 20-mph crash is about 5%, while it goes up to about 50% at 35 mph.

  6. A friend of mine, who's blind, has been aware of these issues for quite some time. Hybrid and electric vehicles are especially dangerous to blind people, who use the sound of car engines to navigate their way across the street. Speed-actuated noisemakers (that turn on whenever the car is running on battery-only) have been the proposed solution for hybrids. I'm not sure what the solution is for full-electrics, but the Leaf's system sounds almost more annoying than traditional ICE cars.

  7. We should institute a mandatory hearing test for bicyclists and pedestrians before allowing them on the streets or sidewalks. Obviously the onus is on the person on the outside of the car to hear it and react to it.

  8. Hybrids dont have to make annoying beeping noises. They can make noises we already associate with electric propulsion.

    Take for example, this Boston streetcar

    Or the classic jetsons wooosh

    And yes, this is absolutely necessary.

  9. Thanks for all the comments!

    I agree that the Leaf's system is annoying, but I think there needs to be some sort of artificial noise to address this issue. It might take some experimentation to find sounds that do the job without being excruciating to listen to.

    That's what focus groups are for right? :)

  10. Overlooked are the Prius owners who are too busy feeling morally superior to notice the pedestrians and bicyclists, who incidentally are doing considerably less environmental damage.

  11. Jeez, this seems a no-brainer.

    Tweak the design of deer whistles, so as to make them work at lower speeds, and extend the ban on cell phone use in motorized vehicles to prohibit in-ear and headphone use by ALL users of public thoroughfares, excluding riders on public transit.

  12. Our city is about to switch to hybrid buses. Now I'm getting a little nervous.

  13. @ Daniel,

    You may not have too much to worry about. This study isn't specifically focusing on hybrid buses. We have some in Southern California and at least the ones I'm familiar with don't lack for sound, even at low speeds. It's always worth studying though.

  14. Less smog, more smug...I'm low on fuel -- any loose change?

    Prius owner

  15. @Daniel -- city buses are already creepily silent and often surprise cyclists because the engine is in at the rear of the bus. They make that godawful roar only *after* they pass you.

  16. On one hand I can see the fear that blind citizens might have about quieter cars, but I also have to wonder if hybrid vehicles are merely an easy target in this case. What about the myriad other silent menaces out there, e.g., unleashed dogs, bicycles, children running about, joggers pushing strollers while wearing earphones? I claim that a quieter city is anything but creepy or dangerous - it is a sign of improvement and movement toward a healthier way of living. We seem to have become so accustomed to being constantly immersed in sound (iPods and their cousins, TV as sonic background, constant cell phone chatter, motorcycles with the ego-enhancing roar, etc.) that we can no longer imagine a peaceful outdoor environment that is not wilderness. If a study indicated increased danger for our deaf citizens, would haters of hybrid vehicles also support strobe lights flashing everywhere that risk was present? Will the completely risk free city of the future be an even more dehumanizing cacophony than it is today?

  17. I'm all for peaceful outdoor environments. But for it to be peaceful in more than an aesthetic sense, we do need safety for pedestrians and cyclists. The injury and death stats were truly horrifying even before hybrids came along, so to increase them seems intolerable to me.

    I don't hate hybrid cars. I just think they need to take responsibility for this extra problem they cause, so that we can enjoy what's good about them without creating a new problem. If they just made as much noise as a normal ICE vehicle at low speeds, that would reduce the risk.