Don’t worry, hybrid cars won’t make world noisier

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, as mentioned in a June 2 Star-Bulletin story. But as a scientist studying the problem and adviser 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.

The Pedestrian Safety Enhancement Act of 2008, introduced last month, proposes a two-year study determining the most practical way for hybrid and electrical vehicles (EVs) -- cars that are functionally silent at slow speeds -- to provide nonvisual cues for pedestrians. The solution likely will establish a minimal sound level for these cars. The automotive industry will then have two years to incorporate this change into new vehicles.

Sound noisy? Well, it isn't, and here's why. First, hybrid and EVs are functionally silent only when traveling in electric mode below 20 mph. Faster than that, and all cars produce enough tire and aerodynamic noise to be audible from a safe distance. Of course it is at slow speeds that cars are closest to pedestrians, whether in parking lots or backing out of driveways. But it is only at these slow speeds that some change is necessary.

Second, only a subtle enhancement of sound will be needed. Hybrids will not beep or chirp or produce an alarm. The enhancing sound, used only at slow speeds, likely will be either the simulated sound 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 will 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.

The human brain is exceedingly sensitive to approaching sounds. Research shows that when you hear a sound approach -- versus recede or remain stationary -- brain regions associated with attention and motor action are quickly recruited. Our brains have been designed to use approaching sounds to avoid hazards. This is true of everyone's brains, blind and sighted alike.

This sensitivity of the brain likely means that we all use car sounds to keep us safe, even if we are unaware of doing so. The auditory system often works at an implicit level in warning of nearby dangers, allowing us to concentrate on more conscious tasks. Your ability to safely cross a parking lot while talking to a friend, manage your children or daydream is facilitated by this implicit auditory warning system.

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.

There are not yet definitive data showing that hybrids are involved in more pedestrian accidents. There are data, however, suggesting that a majority of hybrids' early adopters are particularly conscientious drivers. But as hybrids and EVs 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 pre-emptively.

If you've not yet been surprised by the seemingly spontaneous appearance of a moving hybrid in a parking lot or driveway, you will be. Let's hope that when this happens, neither you nor the driver is talking to a friend, managing children or daydreaming. Better yet, let's hope you'll soon hear that hybrid make just enough quiet sound so that you're not surprised at all.