A regulation to limit diesel emissions took effect in Allegheny County this week, and health department officials and local environmental leaders urged residents to help enforce it.

"It's not something where you're going to have a policeman there saying this [is a violation], but it's peer pressure," said Roger Westman, air quality program manager for the Allegheny County Health Department.

"It's also going to be enforced by complaints."

Beginning this week, operators can't idle their diesel-powered road vehicles, like trucks and buses, for longer than five minutes, or they will face fines of up to $500.

The rule is similar to last year's ordinance limiting unnecessary idling from diesel-fueled school buses.

The new air quality regulations are part of a larger effort to get the area's air quality standards on par with U.S. Environmental Protection Agency standards, said Guillermo Cole, health department spokesman.

Residents can report violations to the health department at 412-687-ACHD.

Operators are exempt from the regulation when, for example, they pick up passengers, warm up engines or when they need to use the heater or air conditioner while sleeping in the truck cab.

The county is targeting diesel exhaust because it contains harmful toxins and carcinogens.

In Pennsylvania, 1,170 deaths were connected to diesel particles in 1999, according to a 2005 report from the nonprofit Clean Air Task Force. The particulates can carry toxic chemicals on their surfaces and can be inhaled into the lungs, Westman said.

The county worked with the Group Against Smog and Pollution environmental group and with trucking businesses to craft the regulation.

Rachel Filippini, director of GASP, said the organization is pleased with the new regulation, but that enforcement will come from residents.

"Citizens are going to play a key critical role in helping to enforce this," she said. "They're the ones walking down the street or in front of the school. They see the idling."

The county plans to work on another regulation limiting idling from off-road diesel-powered vehicles like earth-moving equipment and marine vehicles.