Members of the European Parliament have voted to make ‘Acoustic Vehicle Alerting Systems’ mandatory for all electric and hybrid vehicles in 5 years time.  But is this a good idea? I have a personal reason to question whether the claims of improved road safety are right.
The legislation has arisen because there are fears that hybrid and electronic vehicles are too quiet at low speeds, making it hard for pedestrians to hear them coming. Companies are experimenting with playing noises from loudspeakers hidden under the hood to alert pedestrians. But what sound should they use? Why, something familiar that immediately makes pedestrians think “vehicle.” Here is the space-age hum that Nissan has opted for:
In one scientific experiment, however, people preferred the noise of an internal combustion engine over hisses, hums, and whistles.  There is a legacy of old sounds surviving from obsolescent technologies. As a correspondent to New Scientist wrote, “Imagine if this concept of familiar sounds had been developed earlier. Would cars all make the sound of horses’ hooves instead of the new fangled and confusing drone of an internal combustion engine?” 
So why am I against the use of alerting sounds on electric cars? It might surprise you to hear it has nothing to do with my work as an acoustic engineer and the lost opportunity to reduce noise levels in cities. I would rather electronic cars were quiet because I think that my commute would be safer.
I am currently recovering from a broken shoulder caused by someone stepping off a pavement in front of me and a fellow commuter who were using silent vehicles (bikes). One of the hazards of riding a bicycle in a crowded city is that pedestrians sometimes rely too much on their hearing and don’t look out for cycles. I would prefer electronic cars to be silent because it might encourage pedestrians to be more observant.
I’m not an expert in road safety, but I fear that alert sounds are an engineering solution that is overlooking behavioural changes by drivers and pedestrians. A study in Germany showed that drivers of electronic vehicles adjust their evaluation of noise-related hazards, and concluded that the ‘dangers associated with low noise emissions might be less significant than previously expected.’ 
The evidence on whether electronic cars cause more accidents is mixed. A study in the US showed hybrid cars were involved in more low speed crashes with pedestrians and cyclists than would be expected from the number of hybrid vehicles on the road. But in Japan and the Netherlands no increased risk was seen. 
What do you think? Should electronic cars make artificial noise?
 P. Nyeste and M. S. Wogalter, “On Adding Sound to Quiet Vehicles,”
in Proceedings of the Human Factors and Ergonomics Society 52nd Annual
Meeting—2008 (Human Factors and Ergonomics Society, 2008), 1747–50.