It’s not terribly hard to understand why trucks have traditionally gotten terrible gas mileage. They’re big, heavy, and use big engines to make the kind of power needed for towing. Compared to a more aerodynamic sedan with a smaller engine, the typical truck is at a huge disadvantage for fuel economy. Then again, most people don’t buy trucks to save money on gas, so it’s a sacrifice most owners are happy to make.

In recent years, however, gas mileage in trucks has gotten significantly better. Economy cars still have an advantage, but you don’t have to feel nearly as bad about the environmental damage a new truck causes. Well, unless you modify your truck to circumvent emissions controls. Then you really should feel bad.

Come on, it can’t be that bad

If we were talking about a truly small number of modified trucks spread throughout the least populated areas of the U.S., then it probably wouldn’t be nearly as big of an issue. Individual responsibility can only do so much good, and conversely, individual irresponsibility can only do so much damage. But the amount of pollution these modified diesel trucks spew is absolutely mind-blowing.

That’s not an exaggeration, either. There are probably a few environmental scientists who already knew how bad the situation is. But for most people, the damage certain trucks do to the environment will be an order of magnitude worse than they would have ever guessed.

The reality of trucks dodging emissions controls

As ArsTechnica recently reported, the Environmental Protection Agency’s Air Enforcement Division published a new study showing the impact of truck modifications. In short, the pollution coming from modified diesel trucks rivals the Volkswagen diesel emissions scandal that cost the German company billions of dollars. So yeah, it’s bad.

According to the report, the EPA estimates there are about 550,000 trucks have been modified to pollute above legal limits over the last 10 years. That works out to about 15% of diesel trucks, which is pretty significant in the grand scheme of things. Why? Because they don’t just run dirty. They run really, really dirty.

Modified diesel truck pollution by the numbers

The EPA report estimates that modified diesel trucks are responsible for an additional 570,000 tons of NOx and 5,000 tons of diesel particulate pollution over their lifetime. Those numbers probably don’t mean much to most people, but according to the EPA’s calculations, “due to their severe excess NOx emissions, these trucks have an air quality impact equivalent to adding more than 9 million additional (compliant, non-tampered) diesel pickup trucks to our roads.”

And it’s not like the danger of that pollution is in question. The same ArsTechnica article cited above also referenced a study that linked diesel pollution to more than 4,000,000 premature deaths. Those numbers don’t include the impact on crops, birds, fish, or game, either. If those pollutants kill people, it’s probably also safe to assume they aren’t great for anything else that needs air to live.

Emissions tests work

If everyone lived in their own environmental bubble and didn’t have to worry about the damage their modified diesel trucks did to others, that would be one thing. But that’s also not how the world works. Individual actions have consequences for other people, and while state regulations may not be perfect, the EPA’s report also shows they’re an important part of combatting pollution.

In North Dakota, for example, it estimates that more than 18% of diesel trucks have had their emissions controls completely removed. California, a state that requires regular smog tests, that percentage drops to a little less than 2%. So while it may be a little inconvenient to get a vehicle tested, at least there’s proof those tests improve air quality and lead to fewer premature deaths.