An unintended consequence of electric and hybrid cars was reported earlier this year: these environmentally-friendly cars are a danger because they don’t make enough noise. But now Lotus Engineering have come up with a way to add ‘vroom’ to a hybrid car.

The main concern with these quiet cars has been for the vision impaired, but children and distracted pedestrians, as well as cyclists, are also at risk. According to the Daily Mail “A study at the University of California found that a petrol or diesel car could be heard 36ft away but a Prius was not heard until it was 11ft from blindfolded volunteers.”

So to increase the noise Lotus have outfitted a Toyota Prius “with a waterproof speaker near the radiator that blares simulated yet realistic engine sounds to let pedestrians” (Wired).

Lotus says “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… It is all completely automatic and the driver hears almost none of the additional sound.” [lotus]

Ironically, the technology is adapted “from technology previously developed to block outside noise from the inside of its cars”, says the Independent.

The ‘voice’ is based on recordings of a “suitable donor engine”