It's a sign of the times, but it's not always followed.

"SHUT OFF ENGINES. NO IDLING," says the sign in the Business Loop of the University of Utah campus. But the Deseret News observed Utah Transit Authority buses on Tuesday and counted nine in the Business Loop area, which is designated as a UTA bus waiting area. Six were observed idling.

The average idling time was nine minutes; the median time was 15. One bus idled for as long as 18 minutes.

Buses not only idle at the U. but also at the Salt Lake Central Station, 250 S. 600 West, and on the southeast corner of 100 South and State.

UTA has a policy that prohibits idling engines for more than 15 minutes, UTA spokesman Gerry Carpenter said, with some exceptions to the 15-minute rule for passenger comfort and safety.

The signs at the U. have been in place for about a year and are "there to remind the drivers to be reasonable about it," said Alma Allred, director of commuter services. "Some of them don't do a very good job. And others do a good job."

Idling causes noise and air pollution, and critics note the environmental benefits of mass transit can be partly reversed by idling. "We live in a contained air shed and have frequent problems with air quality," said Brenden Kendall, a doctoral candidate at the U. researching sustainability on campus.

Idling wastes gas, said Matt Carlile of the Utah Department of Environmental Quality. "If you're idling, you're pushing out emissions from your vehicle," he said.

Unlike passenger vehicles, most of which burn gas, most UTA buses run on diesel.

"Diesel vehicles emit more particulate matter, PM 10 and PM 2.5, which are fine particles," said Peter Verschoor of the Utah Division of Air Quality, describing particulates that are less than or equal to 2.5 and 10 micrometers in diameter. "Diesel vehicles emit less volatile organic compounds" such as methane or formaldehyde, than gas vehicles.

The U.S. Environmental Protection Agency is concerned about particulates that are PM 10 and smaller, "because those are the particles that generally pass through the throat and nose and enter the lungs," according to the EPA's Web site on the subject, www.epa.gov/particles/. "Once inhaled, these particles can affect the heart and lungs and cause serious health effects."

UTA's idling policy attempts to balance the environmental effects of idling with passenger comfort and safety, Carpenter said.

When drivers cut bus engines, air conditioning, heat and lights are also cut. That can make passengers uncomfortable on hot and cold days, and actually discourage people from riding. And without lights, buses can be unsafe at night. That's why UTA allows exceptions to the 15-minute rule, Carpenter said.

UTA has placed supervisors at the Salt Lake Central Station and in other locales where buses wait to enforce the 15-minute rule.

Don't automakers use technology on buses that allow heat, air conditioning and lights to run when the engine is cut?

"The bus manufacturers are getting better all the time," Carpenter said. "If we had that option, I'm sure we'd use it."

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