In the opening of Steven Spielberg’s 1971 film Duel, an impatient salesman gets stuck behind a rattling, soot-belching tractor-trailer on a lonely stretch of California highway. Just before the truck’s driver is revealed to be a homicidal maniac, the salesman has time to gripe about the vehicle’s billowing emissions. “Talk about pollution,” he coughs as he is enveloped in the rig’s thick, black smoke.

Pollution in the trucking industry has long been a public issue, and it’s one that certainly didn’t end when the first federal emission limits were introduced in 1974. For good reason: heavy- and medium-duty trucks, which include everything from ambulances and garbage trucks to cement mixers and semis, make up nearly a quarter of all US greenhouse-gas emissions from transportation, according to the US transportation department.

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