Bigger, heavier, more efficient: A deep-dive on cars in the United States (2024)

One of the biggest culture shocks for Europeans going to the US is its cars. They’re bigger, heavier and people drive everywhere. In many parts of the country, walking is not an option. There is no pavement to walk on.

Yet the world continues to move closer to the US model of driving. As I’ll show in a future article, cars across the world are getting heavier and bigger too [update: I’ve now published this post here].

I wanted to understand what’s happening with cars in the United States – not least because it’s a big chunk of the world’s transport sector (its material use, oil consumption, and CO₂ emissions), but also because the rest of the world is following its lead.

I took a deep dive into the data on how cars have changed since 1970. Here’s what I found:

• Cars are getting heavier and bigger. This is because more people are buying SUVs, but also because the medium non-SUV car is getting bigger too.

• Fuel economy in the US has improved: the number of miles you can get per gallon of fuel has nearly doubled since 1975.

• This means driving one mile emits half as much CO₂.

• Yet the total amount of CO₂ emitted has not fallen. This is because the amount of miles driven in the US has outstripped improvements in CO₂ efficiency.

Cars in the US are getting heavier

Let’s start by looking at how cars have changed physically over the last 50 years. All of the data I’ve used for this analysis comes from the US Environmental Protection Agency (EPA).

In the chart, we see the average weight of cars since 1975.

Cars today are the heaviest they’ve ever been – the average American car today weighs around 4300 pounds (that’s 1950 kilograms, or nearly 2 metric tonnes). But this increase hasn’t been linear. Cars in the 1970s were big and heavy, then they shed some weight through the 1980s before increasing again.

When I first saw this data I found it hard to believe. Did 1970s cars really rival the weight of cars today? I was born in the mid-1990s, so have little concept of what cars in 1970s America looked like.

But a quick google and it started to make sense. The popular Cadillac Coupe Deville (pictured below) weighed 4200 lbs (or 1900 kilograms). The Ford LTD and the 1970 Dodge Challenger were just shy of 4000 lbs.

Pickup trucks were also pretty popular – at least as popular as they are today.

At least until the 1970s oil crisis hit, big gas-guzzlers were the popular cars of the day.

The weight of cars fell by 20% through the 1970s and ‘80s, reaching its low point in 1987. But since then, cars have been an almost unstoppable bulking period. Average weights have increased by one-third.

Sedans are getting heavier, but Americans are also moving to SUVs

There are two reasons why the average car has gotten heavier.

The first is that a medium car (known as a ‘sedan’ or a ‘wagon’) has gotten heavier. The second is that there has been a big shift from sedans to SUVs and large SUVs (known as ‘truck SUVs’).

In the chart below, we see how the production share of each type of vehicle has changed over time. In the 1970s, more than 80% of the market was taken by sedans. The rest were pickup trucks.

But in the last few decades, the market has become dominated by large SUVs. 45% of sales in 2021 were truck SUVs, compared to just 25% for sedans.

The increasing weight of cars makes sense from the chart below. The weight of the blue segment – the sedans – has crept up. In fact, the average sedan is about the same weight as a small SUV. But more and more people are also buying truck SUVs which are around 25% heavier than a medium car.

The increase in sedan weight was like an athlete bulking in the gym. The move to SUVs put that athlete on steroids.

Fuel economy has improved, but not as much as it could have

The average car in the US today gets about twice as many miles per gallon as it did in 1975. Then, cars were only getting around 13 mpg. Today, this is almost 26 mpg.

That is, of course, a massive improvement. But not as good as it could have been.

As we see in the chart below, sedans get around 32 miles per gallon. Large SUVs get just 24 mpg – one-third fewer. Pickup trucks get a meager 12 mpg.

So, yes, fuel economy has improved across all vehicle categories. In fact, a small SUV today is much more efficient than the average sedan from the 1980s, 90s, or early 2000s. And large SUVs beat sedans from the 1980s. But if the US had resisted the allure of these large SUVs and pickup trucks, fuel economy could have increased by a lot more.

Driving a mile emits half as much CO₂ as it used to

The story of CO₂ efficiency is a close reflection of improvements in fuel economy. The amount of CO₂ you emit in driving one mile, after all, depends on how much fuel you burn (and what type of fuel you’re burning).

Driving one mile today emits half as much as in 1975. Then, you’d produce around 680 grams of CO₂ per mile. In 2021, this was 330 grams.

Again, that’s an amazing improvement but it could have done even better.

Large SUVs emit more than a third more than the average sedan. Pickup trucks emit more than double.

The USA’s obsession with big cars has sacrificed a lot of gains in fuel economy and CO₂ savings.

CO₂ emissions from passenger cars have increased but could have fallen by at least 20%

If cars emit half the CO₂ per mile that they used to, surely US emissions from passenger transport have been falling?

Unfortunately not. This is because Americans drive a lot more than they used to.

I took a look at the US Bureau of Transportation Service’s data on road mileage. Since 1975, the number of passenger miles driven has a little more than doubled [the total increase in mileage has been a bit more than that: more like a 2.4-fold increase].

If total miles driven have approximately doubled, and the amount of CO₂ emitted per mile has halved, this would mean emissions from road transport have stayed roughly the same.

You might think that’s not a terrible result. But the US has missed a golden opportunity to reduce emissions. It could have cut them significantly in a few ways.

The first is by simply driving less. This, of course, doesn’t happen on its own: it needs good city and infrastructure design; walkable cities; and good public transport. The average American drives around 40 miles per day, twice as much as the average Brit.1

The second is that – as we’ve just seen – the US could have improved its fuel economy and CO₂ efficiency a lot more. As an example, let’s imagine it had stuck with a fleet of sedans rather than moving to large SUVs. If its CO₂ efficiency trend had followed that of sedans, its emissions from passenger transport would have fallen by around 20%.

That is no hardship: Americans would have been driving as much as they do today, and the size and weight of sedans are almost the same as small SUVs. Big cars by global standards.

Fuel and carbon efficiency have improved, but the US is still a global outlier

Technologically, it’s pretty cool that bigger, heavier, more powerful cars are more efficient than standard, uninspiring models of the past. Gains in fuel economy and carbon efficiency are impressive. We should acknowledge that.

But these gains are not unique to the United States. These changes have, and are, happening across the world.

On the global stage, the US looks much less impressive. It gets half the miles per gallon, and emits more than twice the CO₂ per mile than most other countries in the world.

I’m going to look at these global comparisons in a future post [update: I’ve now published this post here].

As is the case with most measures of improvement, we should first acknowledge that progress has been made. But also ask the important question of “compared to what”?