Mayor Rocky Anderson signed an executive order this week that, save for emergencies, limits idling in city-owned vehicles - or private cars on city business - to five minutes.
The mayor's office notes more than 50 percent of air pollution in Utah comes from mobile sources and says Salt Lake City can play an important role in reducing that amount.
Anderson's environmental adviser, Jordan Gates, said Friday the move blends with broader strategies to improve air quality, encourage alternative fuels, reduce driving, bolster alternative transportation and reduce greenhouse-gas emissions.
"We've been acutely aware that we have worsening air quality. Every year, the valley becomes more polluted and smoggy," Gates said. "We want to eliminate at least the localized effects."
Gates added that, when people idle, they contribute to pollution and don't even get a trip out of it. "So it's even more wasteful - we like to say you're getting zero miles per gallon."
Patrick Thronson, spokesman for the green-conscious Anderson, said enforcement of the order and punishment for violations would be up to individual department supervisors.
"It would likely include such things as warnings and possible loss of privileges if violations persisted," Thronson said.
City Councilman Dave Buhler, a mayoral candidate, backs Anderson's edict, given that it exempts police and other emergency vehicles.
"I'm all for doing whatever we can to decrease air pollution," Buhler said.
According to the California Energy Commission's Consumer Energy Center, idling for five minutes consumes as much fuel as driving for about 2.5 minutes and idling for one hour burns an entire gallon of gasoline.
Thronson said he hoped people would take seriously the warnings to help the Salt Lake Valley comply with the Clean Air Act. The Environmental Protection Agency raised standards on particulate matter 2.5 pollution in 2005, and Gates warned the city could fall out of compliance.
"That would seriously halt economic activity" for businesses that manufacture products or consume amounts of fuel but want to come to Utah, Gates said.
As far as idling goes, Thronson encouraged residents to turn their cars off as well.
"Clearly idling is a wasteful practice," he said. "It's bad for vehicles, and it's something that all Salt Lake City residents should be aware of and try to eliminate in each of their own personal lives."
Rosemary Winters contributed to this story.