Which likely was very polluting, because thanks to bitching by the trucking industry, they get a pass on emissions via "gliders."
They can buy a brand new truck sans engine and drop some terribly polluting piece of crap from several decades ago and bypass all modern emissions regulations.
Tomayto, tohmahto.
The SCR/EGR/DPF regime that's been forced upon truck mfrs is at the ragged edge of reliability and maintainability, not to mention its effects on fuel use. So that regulators who've never heard of Pareto optimization can pursue cutting the final 1% of the emissions that a truck from the 1960s would have.
One badly-tuned mid-80s F700 can produce more particulates in a day than a brand-new diesel truck will in its lifetime, but somehow, the priority is not making it easier for the owners of forty-year-old equipment to update to the standard of...2004, but rather to decrease the number of milligrams per tank (at $infinity cost) of soot that a brand-new engine is producing.