The sound of cars

Traffic noise is a problem, and electric vehicles could make things worse.

Published in

The Startup

6 min readJun 28, 2019

There’s so much being written about the coming age of autonomous electric vehicles (AEVs), with disagreement about whether it’s a good thing or bad, whether it’ll happen sooner or later, or even whether it’ll happen at all. But one aspect that doesn’t come up much is noise. It’s easy to see why. Everyone knows electric that vehicles are quiet, maybe even too quiet. So if we have a problem with traffic noise, EVs must be the solution, right? Just the opposite is true.

There are three points I want to make in this post: (1) All cars make noise. (2) This noise harms people. (3) AEVs won’t solve this problem, and may even make it worse.

Tire/Pavement noise is the loudest source of traffic noise at speeds above 25 mph.

Close your eyes.

Try this — stand next to a road or street with moving traffic. Close your eyes and listen to the cars as they pass by. Can you tell if a passing car is electric or gasoline-powered? You probably can’t, because, despite what you may expect, they sound surprisingly similar. We don’t normally listen to traffic this way. We may notice when a motorcycle, a truck, or a bus pulls away from a traffic light, and accelerates through its gears. It’s loud! That’s the sound we imagine when we think of traffic. But that’s not the sound we are hear most of the time. What we actually hear is the sound of tires on pavement. The faster a car goes, the louder that sound becomes. At a steady speed of 25 mph, the sound of tires on pavement becomes dominant. And for every ten-miles-per-hour increase in speed, that sound becomes twice as loud. It makes little difference if the car is a twenty-year-old Corolla or a new Tesla — the sound you hear is mostly the rubber meeting the road.

So what?

You may be thinking “So what?” Actually, the sound of traffic causes a lot of harm to people. Here’s what I’ve learned: in Europe, 50,000 people die each year from heart attacks and strokes linked to rail and road transit noise. … Wait — what? Can that be true? Why have I never heard of this? That’s twice the number of Europeans killed in traffic accidents (25,000 last year)! What are the numbers for here in the United States, or the rest of the world? Good question, but not one that’s easy to answer. Apparently no one is keeping track.

I was able to find articles, here and here, describing strong correlations between traffic noise and a host of health problems, including heart attacks, strokes, obesity, diabetes, depression, and others. While these studies find that traffic noise is a serious public health concern, and that something must be done about it, they fail to quantify the problem by estimating how many people die as a result. There’s no suggestion of a number like twice the number of people killed in car crashes. You could easily assume that, while it’s a serious problem, it must not be a very big problem, otherwise you would’ve heard more about it.

How does noise cause harm?

We know that noise can lead to heart problems, but exactly how is less clear. In a 2018 article, Time magazine described the results of a new study:

Based on existing evidence, the new review suggests that noise disrupts the body on a cellular level. Specifically, researchers say, it induces stress responses and activates the sympathetic “fight or flight” nervous system. This causes a spike in stress hormones, which can eventually lead to vascular damage.

It’s more than just being annoyed by noise. This biological reaction occurs even if you aren’t feeling stressed. And it’s not something you become adjusted to. The Time article quotes the study’s lead author, Dr. Thomas Munzel, to say “In fact, people’s cardiovascular systems actually seem to become more sensitive to noise — and more easily damaged — over time.” Noise even causes this stress response in your body while you sleep. Your sleep can be disturbed even if you don’t wake up.

One problem with conducting studies on the health effects of noise is separating out the effects of factors such as traffic pollution and other stressors of modern urban life. These are known as confounding variables. One such variable that never seems to be mentioned in the readings that I’ve done for this article is the actual physical danger of traffic. The danger is very real. Over six thousand pedestrians were killed last year in the United States, and many times that number were seriously injured. When we’re walking near traffic, we all know that we’re just steps away from annihilation if we aren’t careful.

Cheaper vehicle miles means more vehicle miles.

Speculation abounds about what our future transportation system might look like. It seems likely that the cheaper and more convenient it is to go somewhere in a vehicle, the more people will do so. And if you don’t need a driver’s license, or have to own a car, then more people can use the system. And every time a vehicle drops off its passengers, it will be driving empty until it picks up riders again. This all points toward an increase in vehicle miles traveled — maybe even an explosive increase.

Consider this: if I need to go from my home to a store to buy groceries, I drive my car on my street once on the way there, and once again on the way back. But with transportation as a service (as with Uber or Lyft today), a vehicle has to come down my street to pick me up, and then back up the street to take me to the store. The process repeats after shopping, with the empty vehicle driving away after dropping me off at home. That’s a doubling of the traffic on my street. A quiet residential area could turn into a beehive of autonomous vehicles buzzing back and forth, transporting people, including young kids or older folks who previously might not have made the trip.

A large increase in traffic seems likely, with a corresponding increase in traffic noise, and the ill health affects that go with it. We’ve evolved a transportation system where it feels safe and comfy to travel alone in our soundproof vehicles, but dangerous and noisy to walk or bicycle on the streets we share with them.

Your point of view — driver or walker?

How believable or important this issue of traffic noise seems to you depends on your point of view. Are you a driver or a walker? It’s not an either-or question. If you’re not a driver, you may not be a walker either, just someone who can’t go anywhere. We live in a century-old system of automobility that is so pervasive we can’t see it. Many of us were born into it and we know nothing else. If you’re lucky enough to live in a city with good public transit, or in a neighborhood with access to shops, and cafés, and health care within walking distance, or safe bicycling range, then you’re very lucky indeed. Because, most of us can’t go anywhere except by car. From inside our vehicles, traffic noise is not a concern. It’s literally an externality.

The problem is not self-driving cars — the problem is cars.

Our world was shaped by the automobile throughout the 20th century. Over the coming decades, the world will be transformed, once again, with the growth of cities and the rise of new systems for transportation. There will be a massive investment of money, material resources, and human effort to accomplish this. We can design and build in new ways, based on what people actually need to flourish — socially, physically, and economically. Or, we can follow the same old pattern of more cars and less physical activity. The price will be the same either way.

Transportation is a cost, not a benefit. Real progress is not having more and more of it, but designing to need less and less of it. In a truly smart world, everywhere you wanted to go would be close at hand.