What are the three things to do before crossing the road? We all had them drummed into us as children: stop, look and listen. That third step, however, is becoming less relevant because today's hybrid and electric vehicles are virtually silent.
Pedestrians can correctly identify the direction of an approaching internal combustion-engined car from 28ft (8.5m) away, found a 2008 study from the University of California, but that falls to just seven feet for an electric vehicle. As a result, pedestrians are 40 per cent more likely to be hit by a hybrid or electric car, according to a 2015 report by the UK charity Guide Dogs which is particularly concerned about the dangers for blind people and their animals.
These safety concerns have prompted legislators worldwide to require electric cars to make an artificially-created noise as an audible warning. Rules were due to come into force in the US in 2014 but have been delayed until 2018. Within the European Union, new cars must comply with regulations by 2019.
Making the right noises
It's an unusual problem for the car industry to have. For years, manufacturers have been reducing engine noise in a bid to tackle sound pollution as roads get busier. Meanwhile, tyre companies such as Pirelli have worked hard to make the rubber meet the road a little more quietly.
Now they have the opposite task. At speeds above 18mph (29kph), tyre noise makes most cars sound the same, regardless of engine. At slower speeds, electric and hybrid vehicles need to somehow announce their presence while they are moving.
Whatever the right noise for an electric car, the choice probably shouldn't be left to the driver. We've all heard mobile phones that 'ring' with song snippets or some novelty ringtone that is hilarious to some and intolerable to others. If we did the same with our cars, the result would be irritating and, more importantly, unhelpful.
It might be amusing to make your car sound like a jet plane or play the latest Justin Bieber song as you cruise through the neighbourhood, but pedestrians need to know that what's approaching is an automobile (and not a jet plane or Justin Bieber). That's why Nissan abandoned early plans to make its vehicles sound like a flock of birds.
Sound advice
In a 2013 report, the US National Highway Traffic Safety Administration stipulated that hybrid and electric vehicles need to make a sound "that pedestrians will recognise as being emitted from a vehicle". That means it should be car-like or predictable enough that people will hear it and think "car" even at low speeds.
The sound also needs to provide pedestrians with a sense of the location, speed and direction of travel of the vehicle. In an article for MIT Technology Review, designer and academic Don Norman wrote that companies were "hiring psychologists, Hollywood sound designers and experts in psychoacoustics" to design noises with the right qualities.
Sounds of the wrong frequency, for example, might echo off nearby buildings and make it hard to locate where the vehicle is coming from. Other noises might simply be irritating. The repetitive beeps or warnings that intone “reversing” on large vehicles are designed to annoy because they need to attract your attention immediately – and then they stop. A noise that plays constantly whenever the engine is running can't be as abrasive.
The leading contender for an industry standard so far is that subtle, high-pitched whine you might have noticed when a Toyota Prius hybrid slips past. It's a synthetic, relatively unobtrusive noise and most companies that have released noise-making electric cars have settled on something similar to enhance pedestrian safety.
The silent treatment
Ford tested artificial engine sounds for its 2012 Focus Electric and found that drivers rejected novelty options, such as Star Wars spacecraft noises, in favour of the one that sounded most like a traditional combustion engine.
In the end, Ford changed its mind and decided to wait until warning sounds are required by law.
“We just don't want to be too hasty because there are a lot of factors that go into it and we also want to balance the sounds so that they are effective but not annoying," said Ford's Sherif Marakby at the time.
Meanwhile, Ford has begun boosting the engine sounds of its combustion-engined vehicles because newer models are quieter. The 2015 Mustang EcoBoost actually plays the engine noise through in-car speakers so that petrolheads can enjoy the soothing engine rumble.
Whatever happens, it makes sense to teach our children to stop, look and listen for some time yet.
