MONTROSE, Colo. — There is a new menace on America’s roads: diesel truck drivers who soup up their engines and remove their emissions controls to “roll coal,” or belch black smoke, at pedestrians, cyclists and unsuspecting Prius drivers.

Sgt. Chris Worthington of the Montrose Police Department here is out to stop them.

“You can hear those trucks across town, driving like idiots,” he said on a recent Friday evening patrol. He is among the first law enforcement officers in the country to be trained at “smoke school” to pick up the skills to police the coal rollers.

He lost sight of one truck cruising in the opposite direction, trailing plumes of smoke. But another, a Ram 3500 fitted with two steel smokestacks, was parked in a Walmart parking lot. The owner, Pryce Hoey, insisted his truck was emissions compliant, but nevertheless agreed to demonstrate its smoke-generating prowess.

“I just wanted something different,” Mr. Hoey said, revving the engine and releasing two black pillars of smoke into the evening air before Sgt. Worthington shut him down. “People who see it giggle. They think it’s funny.”