Lotus' automotive design consultancy has developed 'Safe & Sound' hybrid external sound technology to enhance pedestrian safety for the quiet vehicles.

As just-auto has previously reported, organisations in the US such as the National Federation of the Blind (NFB) has expressed concerns about the potential hazards that hybrids like the Toyota Prius could pose for blind pedestrians.

The NFB said over a year ago it was likely to advocate for state and federal laws or regulations requiring such vehicles to make some sort of sound.

Now Lotus Engineering has developed technologies to synthesise external sound on electric and hybrid vehicles to counteract the growing concern these 'quiet' vehicles pose to pedestrians and cyclists.

A simulation of a real engine sound is used on the 'Safe & Sound' Hybrid technology demonstrator vehicle, making it instantly recognisable that the vehicle is in motion.

Due to the almost silent operation of hybrid vehicles at slower speed when running on electric power, the independent travel of the blind and partially sighted may be put at risk as they cannot hear these quiet vehicles as they approach, making crossing a road or walking through a car park hazardous.

The Lotus 'Safe & Sound' Hybrid technology demonstrator uses a standard Prius, one of the highest volume and most advanced hybrid vehicles, to demonstrate the sound synthesis application and compensate for the lack of engine noise emitted by the vehicle when running on an electric motor. What has resulted is the same environmentally conscious hybrid vehicle, without the potential risk to pedestrians and cyclists, Lotus said.

The solution that Lotus has devised is a novel reapplication and development of its Sound Synthesis technology. This is a part of the company's range of patented active noise technologies which comprise three main systems, Active Road Noise Cancellation, Engine Order Cancellation and Sound Synthesis.

To synthesise the engine sound, a road speed signal is taken from the vehicle and a waterproof loudspeaker system is positioned adjacent to the radiator allowing the sound to emanate from the front of the vehicle. Once the vehicle has passed, the sound is not heard. When the car is operating on the electric motor only, throttle and speed dependent synthesised sound projects a realistic engine sound in front of the vehicle.

The technology was designed around the behaviour of a conventional engine, using an existing engine sound which makes it instantly recognisable with the pitch and frequency helping to identify vehicle distance and speed. If the hybrid's engine starts operating, at higher speeds or throttle demands or lower battery levels, the control system automatically stops the external synthesis.

When the powertrain control system switches the car back to running on the electric motor only, the synthesis controller instantaneously sets the system running again. It is all completely automatic and the driver hears almost none of the additional sound.

In order to generate the engine sound, recordings of a suitable donor engine were made and analysed to establish the characteristic frequencies at different engine speeds. These frequencies were entered into the synthesis controller in the form of a 'voice' which outputs the sound through an amplifier and out through the loudspeakers.

Group Lotus CEO Mike Kimberley said: "The increased acceptance of greener vehicles such as hybrid and electric vehicles is to be encouraged; they have an important role in improving fuel economy and reducing emissions. Our advanced external sound synthesis technology increases pedestrian safety, while retaining the car's environmental benefits. We hope that legislators introduce minimum noise requirements for vehicles to encourage the adoption of technologies, such as ours, which will ultimately increase pedestrian safety."

Clive Wood, transport policy officer at The Guide Dogs for the Blind Association said: "Blind and partially sighted people use the noise of oncoming traffic as a cue for when it is safe to cross a road - if a 'quiet' hybrid electric vehicle is approaching then they will no longer have this cue and are immediately put at risk.

Wood added: "As the leading voice on transport and mobility issues in the visual impairment sector, Guide Dogs believes further research and development is needed to address the issues of identifying 'quiet vehicles' for blind and partially sighted people. The charity recognises the environmental benefits of these vehicles however more consideration needs to be given to the safety implications to visually impaired pedestrians."

Duncan Vernon, road safety manager, at RoSPA (Royal Society for the Prevention of Accidents) said: "Road safety professionals teach children that they can improve their safety by listening for traffic, and the sound of an approaching vehicle is a warning that most pedestrians will use before making the decision to cross the road. New electric engines make vehicles much quieter, so we need to look at ways of ensuring the safety of pedestrians. We welcome innovative solutions which address this."