RIVERSIDE, Calif. — Despite legal challenges, California has an urgent timeline to phase out diesel- and gas-powered vehicles in favor of zero-emission ones. This goes for personal cars as well as huge commercial trucks.

There are even more immediate air quality cleanup efforts.

Heavy-duty trucks make up a relatively small portion of the vehicles on California roads. Yet they represent a major contributor to statewide mobile air pollution. New rules and new referees are coming to make sure they’re running as cleanly as possible.

Miles Mahoney looks at what a vehicle puts out into the air. That’s the job of a referee tester. He works at the first of several inspection sites for the Clean Truck Check program.

Any vehicle you buy new in California has been certified by the California Air Resources Board, or CARB, to meet the state’s emissions standards. A new lab just opened nearby to run the tests needed to make that guarantee.

Mahoney’s job is specifically focused on big trucks that are already out on the road.

“Sometimes you’ll get some people who do some tampering to these kind of things and so we always have to be on the lookout,” said Mahoney.

Next year CARB ramps up enhanced enforcement of the Clean Truck Check program. To reduce emissions, all trucks in the state will have to follow these new rules — kind of like getting smog checks for your car.

Going this extra mile is worth it for a driver like Jaye Morgan.

“Since all the cleaning of not just emissions on vehicles, but some of the other aspects that California has done, has made a major difference. Nowadays, you can drive down the roads and you can actually see the mountain ranges around here,” said Morgan.

The University of California at Riverside’s Bourns College of Engineering’s Center for Environmental Research and Technology will run the state referee program, led by research engineer Tom Durbin.

“The impact is fairly big just by finding vehicles that either need more maintenance or have issues that need more significant repairs,” said Durbin.

He’s saying only some trucks go to the referees — usually the worst polluters. They’re like detectives called in to investigate special cases that could end up yielding big environmental gains.

“I think we all notice it when you’re driving down Cajon Pass and you just see all that brown haze that’s over above all the cities there. You know, the air quality is what it is, and this is one of our ways to protect the air quality,” said Mahoney.

California is requiring all new cars sold in 2035 and beyond to be zero-emission vehicles. Trucks used to transport goods through the ports are under a similar deadline.