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Electric vehicle warning sounds are a series of sounds designed to alert pedestrians to the presence of electric drive vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and all-electric vehicles (EVs) travelling at low speeds. Warning sound devices were deemed necessary because vehicles operating in all-electric mode produce less noise than traditional combustion engine vehicles and can make it more difficult for pedestrians, the blind, cyclists, and others, to be aware of their presence. Warning sounds may be driver triggered (as in a horn but less urgent) or automatic at low speeds; in type, they vary from clearly artificial (beeps, chimes) to those that mimic engine sounds and those of tires moving over gravel. Japan issued guidelines for such warning devices in January 2010 and the U.S. approved legislation on December 2010.〔〔 The European Parliament approved legislation that requires the mandatory use of "Acoustic Vehicle Alerting Systems" for all new electric and hybrid electric vehicles within 5 years.〔 Several automakers have developed electric warning sound devices, and since December 2011 advanced technology cars available in the market with manually activated electric warning sounds include the Nissan Leaf, Chevrolet Volt, Honda FCX Clarity, Nissan Fuga Hybrid/Infiniti M35, Hyundai Sonata Hybrid, and the Toyota Prius (Japan only).〔 Models equipped with automatically activated systems include the 2012 model year Toyota Camry Hybrid, 2012 Lexus CT200h, all EV versions of the Honda Fit, and all Prius family cars recently introduced in the United States, including the standard 2012 model year Prius, the Toyota Prius v, Prius c and the Toyota Prius Plug-in Hybrid.〔 The 2013 Smart electric drive comes with automatically activated sounds in the U.S. and Japan and manually activated in Europe.〔 Tesla Motors, Volkswagen and BMW do not currently include warning sounds in their electric drive vehicles, as all of them decided to add artificial sounds only when required by regulation.〔 ==Background== As a result of increased sales of hybrid electric vehicles in several countries, some members of the blind community have raised concerns about the noise reduction when those vehicles operate in all-electric mode, as blind people or the visually impaired consider the noise of combustion engines a helpful aid while crossing streets and feel quiet hybrids could pose an unexpected hazard. Although a 2009 study found no statistically significant difference in pedestrian crashes involving quiet hybrid vehicles when compared to noisier vehicles when both types of vehicles were travelling in a straight line, it found a doubling of hybrid vehicle pedestrian crashes when reversing or parking etc. at slow speeds.〔 Technical Report DOT HS 811 204〕 This problem is not exclusive to electric vehicles. In 2007 research at the Technical University Munich showed that ordinary vehicles in background noise are often detected too late for safe accident avoidance. The researchers measured the distances of 35 approaching vehicles to a pedestrian in the moment when they just got audible in a stationary background noise. These distances were then compared to the stopping distances of the respective cars and an algorithm was proposed to estimate them based on auditory masking. Research conducted at the University of California, Riverside in 2008 found that hybrid cars are so quiet when operating in electric mode (EV mode) that they may pose a risk to the blind, small children, the elderly, runners, cyclists, and other pedestrians, as they may have only one or two seconds, depending on the context, to audibly detect the location of approaching hybrid cars when the vehicles operate at very slow speeds. This research project was funded by the National Federation of the Blind.〔 The experiment consisted of making audio recordings of a Toyota Prius and combustion engine Honda Accord approaching from two directions at to assure that the hybrid car operated only with its electric motor. Then test subjects in a laboratory listened to the recordings and indicated when they could hear from which direction the cars approached. Subjects could locate the hum of the internal combustion engine car at away, but could not identify the hybrid running in electric mode until it came within , leaving just less than two seconds to react before the vehicle reached their position. In a second trial, the background sounds of two quietly idling combustion engine cars were added to the recordings to simulate the noise of a parking lot. Under this condition, the hybrid needed to be 74 percent closer than the conventional car before the subjects could hear from which direction the cars approached. Subjects could correctly judge the approach of the combustion car when it was about feet away. This result means that under closer to normal environmental noise, a pedestrian would not be able to correctly determine the hybrid's approach until it was one second away.〔〔 A separate 2008 study from Western Michigan University found that hybrids and conventional vehicles are equally safe when travelling more than about , because tire and wind noise generate most of the audible cues at those speeds. Hybrid cars were also tested safe when leaving a stoplight and it was found that under this condition they do not pose a risk to pedestrians. All Prius models used in the study engaged their internal combustion engines when accelerating from a standstill and produced enough noise to be detected.〔 A 2009 study conducted by the U.S. National Highway Traffic Safety Administration found that crashes involving pedestrians and bicyclists have higher incidence rates for hybrid electric vehicles than internal combustion engine (ICE) vehicles in low-speed vehicle maneuvers such as reversing or leaving a parking zone. These accidents commonly occurred in zones with low speed limits, during daytime and in clear weather. The study found that a HEV was two times more likely to be involved in a pedestrian crash than was a conventional ICE vehicle when a vehicle is slowing or stopping, backing up, or entering or leaving a parking space. Vehicle maneuvers were grouped in one category considering those maneuvers that might have occurred at very low speeds where the difference between the sound levels produced by the hybrid versus ICE vehicle is the greatest. Also the study found that the incidence rate of pedestrian crashes in scenarios when vehicles make a turn was significantly higher for HEVs when compared to ICE vehicles. Similarly, The NHTSA study also concluded that the incidence rate of bicyclist crashes involving HEVs for the same kind of maneuvers was significantly higher when compared to conventional vehicles.〔 In September 2010, Volvo Cars and Vattenfall, a Swedish energy company, issued a report regarding the results of the first phase of the Volvo V70 Plug-in Hybrid demonstration program.〔 pp. 3-4〕 Among other findings, before the trial drivers participating in the field testing were concerned about being a danger to pedestrians and cyclists due to the quietness of the electric-drive vehicle. After the test several of them change their opinion and said that this issue was less of a problem than expected. Nevertheless, some test drivers said they experienced incidents of not being noticed while others said they had taken extra care in their driving with regard to this issue.〔〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Electric vehicle warning sounds」の詳細全文を読む スポンサード リンク
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