Hybrids Should Sound Safer

The scoop: The Pedestrian Safety Enhancement Act introduced in April proposes a two-year study to determine how the otherwise quiet hybrid and electrical vehicles can provide non-visual cues for pedestrians, particularly those that are sight-impaired. The solution will likely establish a minimal sound level for these cars. We asked Lawrence Rosenblum, professor of perceptual psychology at the University of California, Riverside, to give us his take.

It's a noisy world, and getting noisier. This is likely why there has been such strong reaction to a new congressional bill designed to examine whether hybrid cars should be made more audible for pedestrians, especially the blind. But as a scientist studying the problem and advisor to the Society of Automotive Engineers, I bring good news. We can have it both ways. Hybrid cars can stay quiet and still provide enough sound to be safe for us all.

Sound noisy? Well it isn't, and here's why. First, hybrid and electric vehicles are functionally silent only when traveling in electric mode below 20 miles per hour. Faster than that, and all cars produce enough tire and aerodynamic noise to be audible from a safe distance.

Of course it's at slow speeds that cars are closest to pedestrians, whether in parking lots or backing out of driveways, and where the greatest danger exists. But it's only at these slow speeds that some change is necessary.

Secondly, only a subtle enhancement of sound will be needed. The enhancing sound, used only at slow speeds, will likely be either the simulated sounds of a very quiet engine (think cooling fan) or of rolling tires. Why these and not beeps or chirps or some other alarm? Well, we're already familiar with the noise an approaching car makes, so the safest sounds are car sounds. What's more, not much sound is even needed.

You have your brain to thank for this. It possesses a disproportionately large number of cells that are sensitive to approaching sounds -- as opposed to receding or stationary sounds. We use approaching sounds to avoid hazards. And this is true of everyone's brains, blind and sighted alike.

Thus, while the proposed bill was initiated by the needs of the blind, a slight enhancement of quiet car sounds at low speeds will be safer for us all. This will be even more true as the mean age of the country increases and more of us start losing our hearing. Perhaps in ten years, we'll be thanking the blind community for making us all safer.

As hybrids and electric vehicles become cheaper and come in more styles (a hybrid sports car appeared this year), a wider range of drivers will be behind the hybrid wheel: a good reason to address the problem preemptively.

And although there are not yet definitive data showing that hybrids are involved in more pedestrian accidents, waiting for concrete evidence of injury or death before addressing an obvious hazard is not a sensible approach. This is especially true when the solution is so simple and unobtrusive. Hybrids don't need to be made loud, they just need to sound safer at slow speeds.

Lawrence Rosenblum is a professor of perceptual psychology at the University of California, Riverside. His book on implicit perception will be published by Norton Press in 2009. His views are not necessarily the views expressed by Discovery. If you'd like to comment, please drop me a line at discoverytech@discovery.com