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.