Trucking engenders passion, and I see it in the engineers you depend on, who seem able to beat just about any challenge that comes along. They slide the big lever into gear and they go. I’m especially impressed by those who design engines.

I admire their ingenuity and their inventiveness greatly. There are good ones and bad ones, I suppose, and we’ve all known engines that weren’t exactly impressive. But collectively, the engineers who deliver your horses are a good bunch. And some of them are simply brilliant.

That’s a good thing, given the Environmental Protection Agency’s continuing insistence that diesel engines get cleaner and cleaner and then cleaner again. And now, for your benefit, more fuel-efficient as well. (The EPA should have started there, in my opinion, but that’s a different column.)

Not to say we should have been free to pollute, but you don’t have to be a tree-hugger to realize that something had to be done.

My first taste of that need was in 1972 when I lived in London, England, for a couple of years. With thousands of diesel taxis, buses, and trucks running around the city, not to mention a zillion cars and a lot of household and industrial smokestacks burning coal, the air was truly awful.

And how about California? Every year through the 1980s and early 1990s I used to go to Anaheim, just south of Los Angeles, for a truck show. But the air was so bad — literally brown — that it was several years before I realized there should be mountains visible immediately to the east. I just couldn’t see them through the haze until one unusually clear day. I was astonished.

London and southern California were worst cases, sure, but they showed us just how bad things could get if we didn’t do something.

In 1988, heavy-duty diesel engines produced about 10.5 grams of nitrous oxides per horsepower/hour. (Forget particulates for the moment.) A big engineering push brought that to 6.0 grams in 1990, 5.0 in 1991, 4.0 in 1998, 2.5 in 2002... etc., etc. By 2010 we had a limit of 0.2 g/bhp-hr for NOx emissions, dropping it by another 5% for 2017. And it goes on.

Think about that amazing accomplishment. From 10.5 to 0.2. That’s about a million percent, isn’t it? And particulate matter is essentially gone. I can literally breathe in diesel exhaust now, and California’s mountains are always visible.

All this was first accomplished by creative fiddling with injection, combustion, and timing alone. Then the engineering teams had to resort to cooled exhaust-gas recirculation and later selective catalytic reduction as well. I remember writing, as we approached 2007, that engineers had ideas about those next steps, and had test engines running, but nobody knew for sure how to do it. Same with 2010 and then 2017. The EPA just said “Get it done” — and they did.

Yes, there’s been much pain along the way, with billions of dollars wasted on downtime and lost fuel economy. Some of that was due to simple chemistry and physics, but to some very large extent, that was the result of unrealistic timelines demanded by the EPA and thus to insufficient testing time — not to design failures.

So as to the engineers, my hat’s off to them.