And now it's time to do the same to gas engines.

It is proposed – the step before it is ordered – that they be fitted with particulate traps, the same equipment that already saddles all passenger vehicle diesel engines made since about 2018 (and many commercial/heavy-truck diesel engines, too). These capture soot particles resulting from the combustion of diesel fuel.

Diesel particulate traps – and Diesel Exhaust Fluid (DEF) injection/after-treatment – have made diesel more expensive to buy and to operate. The traps must be purged – "regenerated" – regularly and DEF added regularly. Diesel fuel is also now more expensive than gasoline. It was the reverse until just a few years ago. The result has been that diesel engines are less appealing to consumers, who once bought them to save rather than spend money. And this – along with the almost-impossibility of complying with ever-more-demanding exhaust emissions standards – is why it is almost impossible to find a new car (or even a light truck) that is available with a diesel engine in the U.S. anymore.