Electric cars are much quieter than conventional cars, so much so that they need to emit fake sounds for pedestrian safety. So in a utopian future world where every car on the road is electric, would pesky road/highway noise be eliminated? This article aims to find out.

Table of Contents

Some background

Electric cars are quieter because they don’t have internal combustion engines which perform noisy conversions of fuel (gasoline) into power (movement energy). Instead, they simply have a battery pack which can efficiently and quietly power the electric motor, which turns the wheels.

So could they reduce the sort of noise that people living near busy roads/highways hear regularly? For example:

Four road noise components

The general noise that we hear from roads/highways is actually a combination of a few different noises:

  1. Internal combustion engine related-noise
  2. Wind passage noise: wind hitting against the moving cars.
  3. Road surface noise: some materials, such as newer tarmac, can be quieter than other road materials. This is why driving on newly laid sections of road often seems smoother and quieter than older sections of road.
  4. Tire noise: different tire designs and qualities result in varying degrees of noise.

These four noise-sources produce different levels of sounds at different vehicular speeds (thanks to research from Purdue and also Central Florida Universities:

Sources of traffic noise in a bar graph, from asphaltroads.org

So wind passage-based noise gets noticeable louder with increasing speeds, compared to engine noise which starts to level off at higher speeds.

Things are, however, slightly complicated by the fact that a human’s perception of sound is not absolute. As in, humans don’t accurately perceive 65 dB of sound to be 23% louder than 50 dB of sound: we might actually perceive this increase in dB sound to be twice as loud (even though it’s objectively less than a quarter louder).

In other words, even though EVs are objectively quieter (as explored below), a road or highway full of electric cars might not seem as quiet as we might assume.

Electric cars and the four noise components

To briefly recap on the above section, there’s four components to engine noise:

  1. Engine noise
  2. Wind noise
  3. Road surface noise
  4. Tire noise

As we’ve already established, (1) is not an issue in electric cars. And as our ‘do EVs need special tires?’ article shows, tire manufacturers are aiming to produce as quiet tires as possible (so as to not ruin the quietness overall of driving an electric car) - so (4) is also reduced in an electric car. I mean, there will be tire noise from an electric car, but it will be less than a conventional, gasoline-fuelled car.

So that leaves the (2) wind and (3) road surface noise - and whilst electric cars are great, they can’t magically control the road surface! But they can control how much noise wind produces when hitting against the vehicle, by designing the electric car to be as aerodynamic as possible, thus reducing the drag coefficient.

This isn’t just for noise benefit: because EVs have less range (and less places to re-charge) compared to gasoline-powered cars, it’s essential that EVs are designed to be as efficient as possible. So the more aerodynamic they are, the less the electric motor has to work - thus saving energy. Audi written a great blog post on this when they developed their e-tron.

So electric cars do actually fare better than conventional cars in three of the four noise components. Plus conventional cars are noisy for other reasons:

  • Worn down - or broken - mufflers can be really noisy
  • Torque and traction control isn’t as good in gas cars, hence tires can be quite noisy when setting off, and when quickly turning a corner

To conclude

In summary, a utopian world full of electric vehicles and nothing else would be quieter:

  • Highways would have less noise from tires, engines (or lack thereof!) and wind passage
  • Local neighbourhoods wouldn’t have the occasional screeching of tires, noisy gear changes and dodgy mufflers that they currently have
  • Gasoline cars idling at traffic lights (producing a constant humming noise) would be eliminated
  • Inner city roads would also be quieter, especially at intersections

But exactly how much quieter is almost impossible to measure because - as mentioned earlier - humans don’t perceive sound changes on a constant scale. Equally, even if all vans and trucks are electric, there’s still going to be a lot of noise from trucks with unstable (or unbalanced) loads, and also garbage trucks.

Hence our utopian world would have less nuisance noise from the roads/highways, but we’d still hear general noise from traffic - along with annoying noises from some trunks and other vehicles!