They run without going anywhere and Palo Alto resident Shelly Gordon Gray believes they should be stopped.

Gordon Gray is leading the city's campaign to adopt an ordinance that would target idling vehicles -- those that stand by while their their engines keep running.

A board member for the local Sierra Club chapter, Gordon Gray was inspired to take up the cause about five years ago, while vacationing in Jackson, Wyoming. She was at a shopping center when she saw a "Please do not Idle" sign.

If a red state can do it, she figured, why can't Palo Alto, a city in a blue state where green pride runs deep and where the streets are filled with tech buses, delivery trucks and solo drivers who are texting or talking on the phone while their parked car emits gases that damage the environment.

It's the lattermost category that for her was the biggest pet peeve, she told the Weekly.

"I think what it symbolizes for me is the indifference that we sometimes have," she said. "We don't think we make any difference in terms of climate. It's someone else's problem and someone else should do something about it."

So earlier this year, Gordon Gray got in touch with Palo Alto's transportation officials, who put her in touch with volunteers for the Safe Routes to School program. In March, she attended a Safe Routes meeting at Hoover Elementary School at which other parents and school officials agreed that the problem is worth addressing. She also found willing allies among students, who enthusiastically took up the cause and, at one point, spent four days monitoring the idling habits of parents picking their children up from Hoover. Over that period, the group counted 162 cars idling for at least a minute and 40 doing so for longer than 10 minutes.

Tanli Su, a Palo Alto High student who serves as youth chair of the local Sierra Club's Climate Action Committee, and her peers made a video explaining the menace that is idling and shared it with teachers and administrators.

"Since children's lungs are still developing, they are especially at risk of developing health issues like asthma," Su said. "The greenhouse-gas emissions from idling cars contribute to this."

Schools aren't the only hotspot in Palo Alto, Gordon Gray said. Cars idle around Stanford and at local shopping centers, where someone may leave the engine running while they run into a coffee shop for a beverage.

Gordon Gray also found allies at City Hall. In June, Councilwoman Karen Holman made a pitch for including an anti-idling ordinance as a component in the city's master plan for reducing greenhouse-gas emissions.

"It's low-hanging fruit," Holman said at the June 5 meeting. "A lot of it is education probably, but having the enforcement mechanism of an ordinance to be able to speak to people about idling and the impacts of that would be most helpful."

While Holman's proposal did not win approval at that meeting, other council members are now on board. Vice Mayor Liz Kniss, Tom DuBois and Eric Filseth have all joined Holman on a colleagues memo urging a citywide anti-idling ordinance, a measure that they said would make a "modest but measurable contribution" to the city's goal of reducing greenhouse-gas emissions by 80 percent by 2030.

According to a Department of Energy estimate, idling accounts for about 30 million tons of carbon emissions in the United States a year. Filseth used that number and, adjusting for Palo Alto's population, concluded that idle vehicles produce roughly 6.2 tons of emissions.

"Some of this is short-duration idling done by vehicles at intersections; such as waiting for a stoplight to change, or in stop-and-go traffic," the memo states. "However, other idling is done at curbside, such as by vehicles waiting to pick up passengers or deliver goods, and may last 10 minutes or more' tech-employee and tourist buses have been observed to idle for even longer.

Among the biggest culprits, according to the memo, are construction vehicles that idle while making deliveries or picking up materials -- a problem made worse by the fact that they use diesel fuels.

There is no good reason, the memo claims, for such extended idling.

"Modern vehicle engines do not suffer wear and tear from simply being turned on and off and now use very little fuel in start-up," the memo states.

The memo, which the City Council will discuss Monday, acknowledges that there are plenty of legitimate reasons for idling -- fire and police vehicles responding to emergency calls; Public Works vehicles operating under "certain specified and detailed conditions"; or health conditions that may require a driver or a passenger to maintain a certain temperature.

These exceptions would be considered in the new anti-idling ordinance. In most cases, drivers would be "required to shut off their engines after two or three minutes of stationary idling, if not in an active traffic path," according to the memo.

The new law would be patterned after similar ordinances in Minneapolis, Salt Lake City and Ann Arbor, the memo states.

By Filseth's calculation, the local ordinance could reduce idling-related emissions in Palo Alto by 10 to 20 percent annually, which is roughly equivalent of taking 120 to 240 cars off the road.

The primary cost of the new ordinance, the memo states, would be the posting of signs at schools, truck-delivery stops and employee-bus stops; education materials and -- potentially -- enforcement. The memo notes that the cost of enforcing is "unclear," but argues that "even just signs and education are likely to have at least some impact."

"A city ordinance requiring drivers to shut off their engines after the more feasible (time) of two or three minutes of stationary idling would make a modest by measurable contribution to our 80-30 goal and improved health conditions at a low cost," the memo states.