Since 2009 the Japanese government, the U.S. Congress and the European Commission are exploring legislation to establish a minimum level of sound for electric and hybrid electric vehicles when operating in electric mode, so that blind people and other pedestrians and cyclists can hear them coming and detect from which direction they are approaching.
In January 2010 the Ministry of Land, Infrastructure, Transport and Tourism in Japan issued guidelines for hybrid and other near-silent vehicles. It is found that warning sounds with similar characteristics as engine sounds are the best countermeasures against these risks . Legislation is expected to be in effect by end of 2012.
In January 2011 President Barack Obama signed The Pedestrian Safety Enhancement Act of 2010 making the National Highway Traffic Safety Administration to conduct a rulemaking to establish a Federal motor vehicle safety standard requiring an alert sound for pedestrians to be emitted by all types of motor vehicles8 that are electric vehicles9 or hybrid vehicles (EVs and HVs). Thus, the covered types of vehicles include not only light vehicles (passenger cars, vans, sport utility vehicles and pickup trucks), but also low speed vehicles, motorcycles, medium and heavy trucks and buses. The rulemaking must be initiated not later than 18 months after the date of enactment of the Pedestrian Safety Act. The implementation starts in 2014 and will be effect by 2017.
The Pedestrian Safety Act specifies several requirements regarding the performance of the alert sound to enable pedestrians to discern the operation of motor vehicles. First, the alert sound must be sufficient to allow a pedestrian to reasonably detect a nearby EV or HV operating at constant speed, accelerating, decelerating and operating in any other critical scenarios. Second, it must reflect the minimum sound level emitted by a motor vehicle that is necessary to allow visually-impaired and other pedestrians to reasonably detect a nearby EV or HV operating below the cross-over speed. Third, it must reflect the performance requirements necessary to ensure that each vehicles alert sound is recognizable to pedestrians as that of a motor vehicle in operation.
In 2011 the European Commission drafted a guideline for Acoustic Vehicle Alerting Systems. The guideline is intended to present recommendations to manufacturers for a system to be installed in vehicles to provide vehicle operation information to pedestrians and vulnerable road users. This guideline is intended as interim guidance until the completion of on-going research activities and the development of globally harmonized device performance specifications.
 National Highway Traffic Safety Administration: Quieter Cars and the Safety of Blind Pedestrians: Phase I Report DOT HS 811 304. April 2010