When cars run on electric power they not only save fuel and cut emissions but also run more quietly. Ordinarily, people might welcome quieter cars on the roads. However, as the use of hybrid and electric vehicles grows, a new concern is growing, too: pedestrians and cyclists find it hard to hear them coming, especially when the cars are moving slowly through a busy town or maneuvering in a parking lot. Some drivers say that when their cars are in electric mode people are more likely to step out in front of them. The solution, many now believe, is to fit electric and hybrid cars with external sound systems.
A bill going through the American Congress wants to establish a minimum level of sound for vehicles that are not using an internal-combustion engine, so that blind people and other pedestrians can hear them coming. The bill's proponents also want that audible alert to be one that will help people judge the direction and speed of the vehicle. A similar idea is being explored by the European Commission.
Although there is little data on accidents, the latest research suggests there is cause for concern. Vehicles operating in electric mode can be especially hard to hear below 20 mph (32 kph), according to experiments by Lawrence Rosenblum and his colleagues at the University of California, Riverside. Above that speed, the sound of the tires and of air flowing over the vehicle starts to make it more audible. The researchers made sophisticated recordings of hybrid cars running on electric power and gasoline- engine cars approaching at 5 mph from different directions. These were played to a group of subjects wearing headphones. The subjects were asked to press one of two buttons to identify which way the vehicle was coming from as quickly and accurately as possible. As expected, they were able to determine the direction of the gasoline-engine cars much faster. When everyday background sounds―like the humming engine of a car that had stopped nearby―were added, the hybrids' direction sometimes could not be detected until they were dangerously close. Both sighted and blind subjects gave similar results. Rosenblum and his colleagues recently repeated the experiment outside in a parking lot. This time, blindfolded subjects stood 3 meters away from the point where the vehicles passed. The researchers found that the hybrid vehicles had to be around 65% closer to someone than a car with a gasoline engine before the person could judge the direction correctly.
What sort of noise should electric-powered cars make? They could, perhaps, beep as some pedestrian crossings do, or buzz like a power tool. Having worked with blind subjects, Rosenblum is convinced of a different answer: "People want cars to sound like cars." The sound need not be very loud; just slightly enhancing the noise of an oncoming electric vehicle would be enough to engage the auditory mechanisms that the brain uses to locate approaching sounds, he adds.
Systems to do this are already being developed. Lotus Engineering, the consultancy of a British sportscar maker, recently signed an agreement with a producer of audio systems to commercialize one. Lotus has worked on a number of hybrid and electric vehicles, and it was while these were being used in its factory that the engineers thought they would be safer if they made a noise.
The system Lotus uses was originally developed for a different reason: to cancel out excess noises inside a car. Sound-cancelling works by analyzing any unwanted frequencies and then producing counteracting ones. Lotus modified its system so that it could produce sounds that change with speed, providing a familiar audible “feedback” to drivers of vehicles with a silent engine. Adding external speakers allows pedestrians to hear the noise too.
It is possible to create a different sound within a car from the one that is heard outside, says Colin Peachey, a chief engineer with Lotus. Manufacturers could create their own sounds according to how they perceive their models. Drivers of electric cars might in the future even be able to select different engine sounds, and maybe download them as we currently do with ringtones for our cellphones.
Although some drivers might want to cruise in an electric car thundering to the sound of a mighty V8 engine, it is not necessary―and traffic police may have something to say about it. Synthesized engine noises could even help reduce noise pollution. For instance, sound from the speakers at the front of an electric car (or the rear if reversing) is highly directional. This means it is more likely to be noticed by pedestrians in front of or behind the vehicle. The noise from an internal combustion engine, however, travels out in many directions―including upwards into offices and bedrooms. Unique engine noises would still be possible. A sound generator has already been planned for one new car, a plug-in electric hybrid in the early stages of production. It will both alert pedestrians and enhance the "driver experience." Since the car will use new technology, perhaps the sound itself should also be new.
1) Pedestrians and cyclists find it hard to hear them coming, especially when the cars are moving slowly through a busy town or maneuvering in a parking lot.
・find it C to do ...「...することがCだとわかる」【形式目的語】
←find O C「OがCだとわかる」【第５文型】
・hear O do 「Oが～するのを聞く」【知覚動詞】
2) A bill (going through the American Congress) wants to establish a minimum level of sound for vehicles that are not using an internal-combustion engine, so that blind people and other pedestrians can hear them coming.
・so that S can do.. 「Sが～できるように」
The bill's proponents also want that audible alert to be one that will help people judge the direction and speed of the vehicle. A similar idea is being explored by the European Commission.
・want O to do「Oが～することを願う、Ｏに～してほしいと思う」
（O = that audible alert）