Can a car be too quiet?

Everyone agrees that electric cars are the future. But they have one big problem - they don't make nearly enough noise. Patrick Barkham reports

Patrick Barkham
The Guardian, Thursday December 4 2008

The noise of an electric vehicle used to be unmistakable - a loud whining crescendo followed the clank of milk bottles. Now, however, virtually silent mass-produced electric cars will soon be creeping down our streets. They eradicate noise pollution, and air pollution, but raise a new problem - for pedestrians, cyclists, and particularly for the blind and partially sighted.
Back when electric cars looked like golf buggies and tootled along at 20mph, the absence of a throaty combustion engine was no great danger. But electric vehicles are now matching ordinary cars in speed, with trials of a 95mph electric Mini beginning next year in the US, and electric sports cars, such as the forthcoming 130mph Lightning, which, it is claimed, do 0-60mph in less than four seconds.
Road safety groups are worried about children and cyclists, who are dependent on listening when changing lanes. Charities for blind people are also concerned. "We're not saying we shouldn't have electric vehicles, but we need to consider the safety implications for partially sighted people and other vulnerable pedestrians," says Clive Wood of Guide Dogs for the Blind. "It would be better to do this now, rather than wait until we have a high number of quiet vehicles on the street."
Andy de Sallis, managing director of Gem electric vehicles, points out that its cars still make a noise through their tyres, and an electric purr. Gem, which supplies vehicles to local governments, businesses and police forces, also fits a warning button to its machines which is less intrusive than a horn but makes a noise like a truck reversing. Wood, however, says that is not sufficient. "It puts the onus on the driver to recognise someone who is visually impaired, and partially sighted people are not always easy to identify. They don't all have guide dogs or white canes."
Wood wants the Department for Transport to investigate the issue and establish a set of minimum requirements for vehicle noise in the UK. In California, where more than 350,000 electric or hybrid vehicles cruise the boulevards, a committee will next year make recommendations about noise-making safety features for electric vehicles which could then be introduced as law by the governor, Arnold Schwarzenegger.
Dan Kysor of California's Council of the Blind, who uses a guide dog, reported several near misses with hybrids. He found them particularly dangerous when they were stationary in traffic because the engine shuts down. "I can sense there's a big object nearby, but because it's not making any noise, I can't tell what it is," he says.
A University of California study found that a petrol/diesel car could be heard 36ft (11 metres) away, but an electric Toyota Prius was not heard until it was 11ft from blindfolded volunteers. "If you're going at 30mph and you've only got 11ft to stop, there is a real danger," says Matthew Reed of Lotus Engineering. He became aware of safety concerns when Lotus made its first electric car. As it was driven around its factory, there were a couple of occasions when engineering staff nearly had accidents because they didn't hear it coming.
So Lotus engineers have re-created external noise by playing a recording of a Toyota petrol engine through waterproof speakers tucked under the car's radiator. The faster it goes, the more sound is emitted. This "external sound synthesis" is not yet in production but Reed says there has been "massive interest" from electric car companies.
It sounds bizarre but according to Lotus's chief noise engineer, Colin Peachey, synthetic noise is far less intrusive than an ordinary engine. In normal cars, engine noise is projected in all directions, particularly upwards. With this system, sound mapping shows it is beamed forwards, delivering noise to the relevant areas ahead of the car's direction - and not into bedroom windows for instance.
But why recreate an engine noise? Why not project birdsong or heavy metal? "Making a noise like a conventional car is the only answer for someone who is partially sighted," says Peachey, who explains that the visually impaired can tell from the level and pitch of an engine sound not only how close a vehicle is, but how fast it is travelling. Until all cars are electric, he says, they need to emit a commonly recognised and predictable sound that won't get drowned out by other engines.
It seems that the purr of the petrol engine - or something that sounds very like it - will probably echo along our streets for a while yet.