Issue: Dec 2011

Guaranteeing Pedestrian Protection: Sound Warning Systems for EVs and Hybrids

by Renee McClellan

Electric vehicles have truly been an industry changing step forward with their use of cutting edge technology to improve mileage and reduce emissions. However, not all of the side effects of electric vehicles are considered good. Japan and the U.S., at the prompting of safety advocates and organizations for the blind, have issued guidelines or have enacted legislation requiring electric vehicles and hybrids to have artificial noises to warn pedestrians that they are approaching. Agencies within the European Union are also investigating similar requirements.

The saying is “Silence is golden.” Well, maybe it is not in this case. According to the U.S. government’s automotive safety agency, hybrids driven at low speeds are twice as likely to be involved in pedestrian incidents as automobiles with conventional engines. Pedestrians often rely on the noise generated by vehicles to know that the vehicle is approaching. Hybrids and electric vehicle that do not have the same noise levels as traditional internal combustion engine cars can, therefore, be a problem for bystanders. This safety issue, known as “hybrid creep,” is particular to electric vehicles and hybrids and is an issue at 20 mph or less only. The issue goes away at higher speeds since the predominant noise used by pedestrians to determine whether a vehicle is approaching at higher speeds is tire and wind noise.

Research has proven that the noise generated by conventional automobile engines helps pedestrians, particularly blind or visually impaired ones, when crossing the street. In 2008, the University of California, Riverside conducted research and found that pedestrians had only one or two seconds to react to a hybrid when operating in electric mode. In the study, it was found by perceptual psychologist Lawrence D. Rosenblum that without any background noise participants could detect a car with a traditional internal combustion engine from 36 feet away. This distance reduced to 11 feet when the hybrid vehicle was used. In a further trial, the sound of two idling combustion engine cars was added to the background noise level. This time participants detected the internal combustion engine car from 28 feet away; however, the hybrid had to be less than three feet away in order to be noticed. The research, needless to say, concluded that hybrids operating at slow speeds in electric mode may pose a risk to the blind, small children, the elderly, runners, cyclists, and other pedestrians.

Rosenblum has repeated his research and added direction of travel to the study. He found that hybrid vehicles had to be approximately 65% closer to a person than a car with a traditional engine before the person could judge the direction the car was approaching from.

In addition, in 2009, the U.S. National Highway Traffic Safety Administration found that hybrids were twice as likely to be involved in an accident involving a pedestrian or bicyclist than a traditional internal combustion engine vehicle when certain low speed maneuvers, including slowing, stopping, backing up, and entering or leaving a parking space, were completed.

It is not just the safety advocates that are worried. In 2010, Volvo Cars and Vattenfall, a Swedish energy company, found that drivers participating in a field test for the Volvo V70 Plug-in Hybrid were also concerned. Some drivers even went as far as to change their driving style around pedestrians and cyclist since they were worried about the quietness of the vehicle.

In January 2010, Japan’s Ministry of Land, Infrastructure, Transport, and Tourism issued guidelines for manufacturers of hybrids and other near-silent vehicles, and on January 4, 2011, the Pedestrian Safety Enhancement Act was signed into law in the U.S. The act does not specify a noise or a speed requirement; however, it requires the U.S. Department of Transportation to establish a safety requirement for an alert sound to aid the blind and other pedestrians to reasonably detect an approaching electric or hybrid vehicle. The U.S. requirement must be finalized by June 2012.
It looks like synthetic sounds on all hybrids and electric vehicles to aid pedestrians and other road users are inevitable. The good news is that, according to Rosenblum's research, the noise does not need to be loud. The brain is more sensitive to noise that is approaching since this type of noise signifies that the person might be in danger. The warning noise used on vehicles can, therefore, be subtle, if it is the correct kind of sound. Rosenblum's research found that carlike noises, such as a traditional engine or the sound of tires rolling, were more useful than chirps, beeps, and alarms which were found to be more of a distraction.

Without standardized tones being required by the various legislations, automakers are implementing their own solutions to alert pedestrians and the driver of an electric vehicle or hybrid that it is slowing down or stopping, backing up, or entering or leaving a parking space. Sounds range from beeps to tones to copies of internal combustions engine sounds to spaceships.

The Nissan Leaf uses a soft whirring sound, Nissan’s Vehicle Sound for Pedestrians. The sound changes pitch as the car accelerates when the vehicle is moving forward. The noise, which was designed with the help of acoustic psychologists and Hollywood sound designers, is a sine-wave that sweeps from 2.5 kHz to 600 Hz. The range was selected so that it could be audible across all age groups. The sound is emitted through speakers that are located in the front driver’s side wheel well. The Chevy Volt uses a subtle chirp, generated by the car’s horn, to perform the same function. The GM system used on the Volt is called the Pedestrian-Friendly Alert System and was developed to alert but not startle pedestrians.

Hyundai’s warning system is called Virtual Engine Sound System (VESS) which generates a synthetic sound that is supposed to represent an idling internal combustion engine. It is closer to something that Rosenblum would probably recommend. Similarly, the Toyota system, called Vehicle Proximity Notification System (VPNS), uses an electric motor sound that rises and falls in pitch relative to the vehicle’s speed.

Other automotive manufacturers are going a step further and developing systems for the driver as well as pedestrians. Fisker Automotive has developed such a system. With the Fisker system, the sound is emitted through external speakers that are mounted in the bumper of the car. The specially developed sound is said to be a cross between one that might be emitted by a racing car and a spaceship. Another offering, the Lotus and Harman International system, known as HALOsonic Internal and External Electronic Sound Synthesis, is a solution that uses the vehicle’s normal audio system and some external speakers to generate engine sounds. The internal sounds change with speed and the use of the throttle to provide the driver with a sense of what the otherwise silent engine is doing. There are four options for engine sounds available with the system. Two of them have been designed to simulate a V6 and a V12 engine.

Automotive manufacturers are not the only ones developing sound systems for electric vehicles and hybrids. There are also solutions on the market that are available from independent companies. For example, Enhanced Vehicle Acoustics (EVA) is a company that is based in Silicon Valley. EVA has developed a technology called Vehicular Operations Sound Emitting Systems (VOSES) that is suitable for after-market use. The system only works when a hybrid is in electric mode and makes the vehicle sound like a quiet internal combustion engine vehicle. The VOSES system solution places miniature audio speakers in the vehicle's wheel wells. The sounds are then emitted in the direction the car is moving. EVA, similar to Rosenblum’s findings, thinks this option is a better solution than tones or chirps because it is less distracting and because the best sounds for alerting a pedestrian of an approaching car should be carlike. By projecting the noise in the direction of travel, the company also thinks that the VOSES system minimizes noise pollution by generating more useful sound information that is targeted in the right direction.

ECTunes is a similar system that only emits sound in the direction it is needed. ECTunes is backed by Energi Horsens, a Danish firm. Finally, RocketAudio Traffic's system prerecords and then simulates internal combustion engine sounds. The system is fully programmable and has the ability to produce sounds for other events within the vehicle such as when the door is closed or the seat belt needs to be fastened.

Not all of the systems available are active systems. Some must be turned on by the driver. Also, not all of the systems address reversing. It is hoped that at least in the U.S. that the Department of Transportation requirements will address all of the vehicle maneuvering situations where pedestrians and cyclist may be at risk. It is also hoped by some that standards will be developed as to the type of noise required to avoid confusion in highly congested areas.

Although automakers and independent companies alike are rushing to develop sounds to alert pedestrians or to enhance the sound of hybrids and electric vehicles for the driver, not all experts agree extra sounds are necessary. Some environmental advocates have questioned the need for the extra tones and are concerned about the extra noise pollution that they will generate in residential districts. Although most recognize the safety issues with the quietness of electrical vehicles and hybrids as being real concerns, they suggest that it would be better to reduce the noise levels of louder vehicles - trucks, buses, and motorcycles - to eliminate the general background noise levels instead of adding additional sound systems to electric vehicles and hybrids. 


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