Palo Alto drivers caught running their engines without going anywhere could be slapped with a fine but will more likely receive a warning under a pending city law aimed at cracking down on vehicle idling.

In a 3-1 vote, the City Council's Policy and Services Committee on Tuesday night signed off on a draft anti-idling ordinance similar to one in Minneapolis, which focuses more on educating drivers than punishing them.

Under the proposed law, which will go back to the council for final approval, police would issue first-time offenders a warning for idling their vehicles longer than three minutes and could hand out $100 to $150 citations to second- and third-time offenders, respectively, within a calendar year.

While the committee doesn't expect that police will likely punish motorists, members believe the proposed law could be a useful tool in changing drivers' behaviors.

If approved, the ordinance will be tested as a yearlong pilot program, then assessed by the council.

The city's push to ban idling cars as a way to improve air quality has been well-supported ever since activists from a local Sierra Club chapter pitched the idea earlier this year. On Tuesday, however, the committee found itself pondering whether to pass a law without any kind of enforcement mechanism after city staff warned that enforcement will be "challenging and of limited effectiveness," according to a report from the office of City Manager James Keene.

Committee Chair Cory Wolbach, who cast the lone vote against the committee's proposal, questioned the value of passing a law that the city can't reasonably enforce due to lack of staffing. He suggested adding an anti-idling provision to city code as an educational tool to gauge whether that would be enough to curb behaviors so enforcement wouldn't be necessary.

Wolbach was curious to see how many drivers would "flip the bird" or ignore police officers, residents or anyone who may say, "Hey, you've been idling your car for 10 minutes. Palo Alto has an ordinance against that."

Vice Mayor Liz Kniss and council members Tom DuBois and Lydia Kou all agreed that having an ordinance that stipulates consequences is good, even if it's one that might rarely be enforced.

"We should have some form of enforcement even if we rarely use it, just for extreme conditions," DuBois said.

Kniss, who serves as chair on the Bay Area Air Quality Management District's board of directors, initially favored an education program over an ordinance with penalties but changed her position.

"It would be embarrassing to go to the next (board) meeting and tell them we turned down the idling ordinance that has been widely touted as something that might help with air pollution," Kniss said. "The more I think about it, the more I think that maybe we have an ordinance, and you don't enforce it. You find other ways to let drivers know they are in violation, just as Minneapolis did, and come back again and look at it after a year and see if it's something that's working."

Keene said he didn't have a problem with the ordinance as proposed since it is clear that it will be a low-enforcement policy.

"It does put us in a predicament sometimes when a citizen in the community sees we have a problem and we're not enforcing it," he said. "You guys will probably get a call ... saying how unresponsive the city staff is, including the city manager."

Keene suggested that the city get "more creative" about what it's trying to accomplish, especially near schools where idling is an issue while parents wait to pick up their children.

He suggested getting students involved in the anti-idling effort through an education campaign.

"We all know from the anti-smoking program, getting kids to bring stuff home and putting it on the refrigerator about smoking being bad actually does have some impact," he said.

He suggested having students give out fake tickets to drivers.

"You don't get a real ticket; you get an embarrassment ticket," he said. "I would be much more disturbed thinking that kids who wanted to deal with health and this sort of thing were sort of calling me out on this much more than if the (police department) stopped me."

In August, council members embraced the idea of creating an anti-idling law to improve health conditions and help the city reduce carbon emissions by 80 percent come 2030, according to a memo authored by Kniss and Council members Eric Filseth, Karen Holman and DuBois.

The council members estimated that idling vehicles produce about 6.2 tons of greenhouse-gas emissions per year. Tour buses, tech shuttles, delivery vehicles and construction vehicles are some of the top culprits.

The pending ordinance lists about a dozen exceptions. These include instances in which a vehicle has to stay still because of traffic congestion or traffic signals; when the driver has to operate a defroster, heater or air conditioner to prevent a health emergency; when the temperature is cold enough (below 40 degrees) or high enough (above 85 degrees) to warrant heat or cooling; or when a vehicle has mechanical problems.

The law also makes exceptions for emergency-response vehicles, private-security providers and armored vehicles that idle in the course of their business.