Warning system for electric vehicles - Security and sound design

The introduction of hybrid and electric vehicles into the world's vehicle fleet has led to a significant reduction in air pollution from road transport. These new vehicles also offer the much-awaited –– advantage of reducing noise pollution in urban environments. They do, however, have the disadvantage of reducing, or even eliminating, a major source of sound information used in particular by pedestrians. These vehicles can be made quieter at low speeds, as electric motors tend to be much quieter than their internal combustion counterparts. Moreover, as tire noise is very low at these speeds, they can end up being hard to hear for pedestrians and other urban road users. This loss of reference points is all the more crucial as silent vehicles share the road with other, noisier vehicles. This situation creates additional risks for pedestrians, especially the blind and visually impaired. Public authorities in various countries (Japan, Europe, USA...), aware of this issue, have set out to solve the problem. Actions, initially launched at national level, have led to this issue becoming a global concern, addressed within the United Nations and, of course, shared by the automotive industry, which is investing in the electric car market. At the heart of this article is the sound solution, as adopted by the regulations. The aim is to reduce the number of collisions between pedestrians and electric or hybrid vehicles. The main questions raised by manufacturers, public authorities and the general public can be summed up as follows: what is a silent vehicle? what are the danger situations? what are the possible acoustic/non-acoustic solutions, for the driver/pedestrian? do we need a sound based on an elementary sound, or a complex sound signature? in the latter case, do we need to adopt a traditional alarm design approach, or deploy a genuine sound design process? what properties must the signal have in order, firstly, to comply with minimum safety regulations, secondly, to meet the functional and ergonomic demands of the problem (emergence, comprehension, interpretation...) and, thirdly, not to contribute to an increase in noise pollution? how can this approach be compatible with acceptability and integration criteria? what are the rules to be prescribed to ensure the required safety, and what are the standardized methods for verifying them?

This article addresses these and other issues, in an attempt to provide a comprehensive approach to the problem from both an industrial and a legislative point of view. It attempts to identify the key points and aims to propose a description and analysis of the problem. In fact, it is organized in four distinct parts: a description of the context, including a description of a silent vehicle, and the identification and description of accident-prone situations;...