As Long as It’s the Right Sound

Lawrence Rosenblum on the hazards of ultra-quiet hybrid cars:

This finding is consistent with a fact many of us have suspected all along: the quietness of slow moving hybrid cars is a danger to all of us—blind and sighted alike. Our auditory systems often work at an implicit level in warning of nearby dangers, allowing us to concentrate on more conscious tasks. Our ability to safely cross a parking lot while we talk to a friend, manage our children, or simply look for where we’ve parked, is aided by our implicit auditory warning system.

In fact, there’s evidence that our brains are exceedingly sensitive to approaching sounds. Research shows that when we hear a sound approach—vs. recede or remain stationary—brain regions associated with attention and motor action are quickly recruited. The auditory brain also possesses a disproportionately large number of cells sensitive to increasing sound loudness: one of the primary cues for perceiving approaching sounds. These brain findings jibe well with perceptual research showing that we consistently over-anticipate the location of approaching sounds. It’s likely that our auditory systems have been designed to use approaching sounds to avoid hazards. If there’s too little sound to effectively engage the system, as is the case with hybrids at low speeds, then any normal distraction becomes hazardous.

But our hyper-sensitivity to approaching sounds can also be part of the solution. It means that only a subtle enhancement of sound should be needed. Hybrids and electric cars won’t need to beep, chirp, or produce an alarm to be audible. Beeps and chirps are likely more distracting than they are perceptually useful. The enhancing sound, needed only at slow speeds, could be either the simulated sounds of a very quiet engine (think cooling fan), or of rolling tires. For purposes of both auditory utility and simple familiarity, the safest sounds are car sounds. And these sounds would be barely noticeable for most of us. Not much sound is needed for the auditory system to warn us about hazards, as long as it’s the right sound.

This entry was posted on Friday, October 9th, 2009 at 6:17 am and is filed under Traffic safety. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

13 Responses to “As Long as It’s the Right Sound”

  1. ChurchyLeFemme Says:

    I read elsewhere ( ) that Nissan has licensed the sound effect from the flying cars in Blade Runner. I found that to be a brilliant solution. It does 2 things: it taps into a great bit of sound design, and it positions their cars as futuristic.

  2. fred_dot_u Says:

    It won’t matter what the sound is, if ambient noise is already so high as to mask it. It can’t be a contest among vehicle manufacturers to make their noise louder than the next one.

    This appears to be another example of masking the real problem. It’s not the vehicle, it’s the driver. Are the drivers of noisy motor vehicles less likely to strike a pedestrian or blind person? No, they aren’t.

    Fix the problem with the driver, not with the vehicle. Put the responsibility squarely on the shoulders of the operator, especially since the vehicle they operate outweighs the prospective victims in all cases.

    If the problem can’t be fixed with the driver, stop allowing them to drive.

  3. Brent Says:

    I can’t tell from the excerpt whether Rosenblum discusses it, but electric cars aren’t completely silent even at low speeds, and at higher speeds are as noisy as gasoline cars (tire and wind noise eventually becomes the dominant sound from most cars). One wonders whether a street environment composed entirely of electric cars, in which their low-speed noise isn’t drowned out by louder engines, wouldn’t allow pedestrians to hear them. I just hate the idea that we would add noise to our city, when electric cars promise a quieter environment.

    In any case, drivers will always remain responsible for safe driving, and parents should still teach their children to look both ways before crossing the street.

  4. George Says:

    As a cyclist and walker I would rather be on a road of all electic cars rather than to smell and inhale the ICE exhausts(and unburned fuel when some driver accelerate in excess when passing me).

    I am all for quiet roads.

    I agree with ‘fred_dot_u’ the problem is the driver.

  5. fred_dot_u Says:

    Thanks for your supportive words, George. Unfortunately, I feel I’ve left out something important. It’s not only the driver, but also the societal development that allows most drivers to avoid the recognition that it is the driver at the root of all this. Of course, if a driver does recognize that the answer is not noise-makers, air bags, roll-over protection, crash-surviveability and does recognize that it’s the driver, that recognition is usually described as “the other driver(s)” and not necessarily the driver in the spotlight, so to speak.

    Just my opinion, your mileage may vary. California mileage may be less.

  6. Yokota Fritz Says:

    I _like_ quiet streets — please no added noise!

    Traffic noise pollution adds to chronic stress leading to heart disease and high blood pressure. Loud pipes (and trucks and cars) do NOT save lives!

  7. Reid Says:


    I agree that driver inattention is a huge problem and kills people. But it’s not going away anytime soon if ever. “stop allowing them to drive” is unrealistic.

    Thus, it is critical that we give our most vulnerable modes (peds and cyclists) the tools to detect (and thus avoid) oncoming danger.

    After all, they have the strongest incentive to avoid collisions with autos; let’s empower them to do so.

  8. fred_dot_u Says:

    I won’t argue for a moment that my comments are unrealistic. I don’t necessarily agree that noise being added to the environment is an answer, however. Recognizing that driver inattention is a problem on the roads appears to be a major stumbling block to all road user safety.

    A curiously well-timed blog entry, as only yesterday, Daytona Beach, FL had an enforcement action “event” supportive of blind walkers. The local paper reported that one driver was stopped by police for not stopping for the crossing blind. Unfortunately, one small article in the paper is unlikely to change much.

    As a commuting cyclist, I have “empowered” myself to deal with inattentive drivers. It’s called FL Statutes that support lane positioning for the cyclist. Part of my own empowerment was taking two LAB classes for cyclists and learning, even after more than 50 years of riding that there are safer ways to ride.

    Educating drivers apparently is considered impossible by many, but educating drivers is really a good part of the solution.

  9. Colin Says:

    If silent cars become more popular, my life as a cyclist will become safer as pedestrians will be less likely to step off the footpath straight into my path without looking.

    Cyclists are silent and travel at similar speeds to that of a “low-speed” car. And yet nobody is saying that cyclists should make a constant noise to warn others, perhaps because in a collision with a pedestrian the cyclist is as likely (perhaps more likely) to be hurt than the pedestrian. In other words, the cyclist is motivated to avoid collisions with pedestrians, whereas motorists are not.

  10. SteveL Says:

    I have some noisy hope freewheels on my bike; their clickety sound acts as a cue to pedestrians that a bike is coming and tends to reduce the #of people who step out in front of me. But still they do, especially on wet days, when people are running round, wearing hoods or holding umbrellas. I can deal with this by predicting it and staying below 15mph in town. Maybe the issue with hybrids is not the fact that they are silent, but that they are still driven round cities at the wrong speeds.

  11. fred_dot_u Says:

    There you are, SteveL. Another person who recognizes that the responsibility lies with the operator of the vehicle, regardless of the sounds or lack of sounds it makes.

    Those individuals who are suggesting to require noisemakers are apparently incapable of recognizing the need for responsibility on the roadways.

  12. Spiderleggreen Says:

    Yeah, for quiet cars that don’t belch smoke. I wonder how an electric Harley would do? Probably not because their goal is to be as loud as possible.

  13. Ted King Says:

    I like the idea of a moderate noise-maker. It might make it more palatable if the auditory signal were linked to a mammal (a warm, moving body that generates an electro-magnetic field) sensor. That sensor could also turn on a heart beat sound (a la ST-TOS “The Mark of Gideon”) at a low level.

    Suggestion :
    In a follow-up post compare the noise produced by antique cars (e.g. Stanley Steamer or Stutz Bearcat) to various modern vehicles. You might also want to include a gas-turbine type powerplant. I believe there have been experimental units produced for engineering studies.

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