San Francisco Department of the Environment

Vehicle Idle Reduction

What is Idling? 

Idling occurs whenever a vehicle’s engine is running but the vehicle is not moving. Drivers commonly idle because they are waiting to pick up passengers, to run the air conditioner or heating, or to power other accessories.

In the United States, idling wastes more than one billion gallons of fuel a year, makes our air dirty, negatively impacts our health and wastes about four billion dollars a year.


Idling Myths

Myth: Cars need to be warmed up by idling before you start driving.

Truth: In modern vehicles, this is not the case. The best way to warm up a vehicle is to begin to drive it.

Myth: Starting and stopping a vehicle damages its engine.

Truth:  The damage that this causes to the engine and battery is negligible. Furthermore, idling an engine means that it does not reach the temperatures necessary to fully combust fuel. The fuel that is left behind clogs up the engine causes problems and can result in costly repairs.

Myth: Stopping and restarting an engine to avoid idling uses more fuel than leaving it running.

Truth: If the vehicle will be idling for more than 10 seconds, it is more efficient to turn off the engine than to leave it running. This is because the fuel burned while idling for 10 seconds is equivalent to the amount of fuel it would take to turn off and restart the vehicle.


Anti-Idling in San Francisco 

The California Air Resources Board has produced two anti-idling measures:

  1. ATCM to Limit School Bus Idling and Idling at Schools: This measure limits school bus idling within 100 feet of a school to 30 seconds maximum and five minutes when not in close vicinity to a school.

  2. ATCM to Limit Diesel-Fueled Commercial Motor Vehicle Idling: This measure limits idling of heavy duty commercial vehicles in California to five minutes. 


Why Does Idling Matter?

Idling is economically inefficient

Idling for just 10 minutes over the course of each day wastes about $250 each year. In other words, for every two minutes a car is idling, it uses about the same amount of fuel it takes to drive about one mile [1].

Idling threatens public health

Idling poses a serious threat to human health. Particulate matter emitted from diesel engines causes cancer, heart & lung disease, asthma and other respiratory and health impacts [2]. Children and the elderly are especially vulnerable.

California has the worst air quality in the nation. In 2005 alone, this pollution caused  premature deaths, non-fatal heart attacks, loss of work days, and restricted activity days for minors [3]. Particulate matter causes 15,000 premature deaths annually in the United States, strains the healthcare system and hinders productivity [4].

The concentrations of these pollutants, and therefore the health risks that they represent, are actually greater inside of the idling vehicles in many cases, providing further reason for drivers to avoid idling [5].

Idling emits greenhouse gases that drive climate change

Climate change is caused by the gradual increase in the Earth’s average temperature and is driven by greenhouse gases, primarily through the combustion of fossil fuels for human uses - the same fossil fuels that we use to power conventional engines in our vehicles. A change of even a few degrees could be catastrophic for humanity, due to melting ice caps and glaciers, rising sea levels, extreme weather conditions and increased spread of disease.


What Can I Do to Reduce Idling?

Light Duty Vehicle Owners:

  • Turn off the engine when parked or stopped for more than 10 seconds.
  • Roll down windows to cool down instead of idling to run the air conditioning.
  • Avoid drive-thrus: park the car and walk inside instead.   
  • Avoid using a remote vehicle starter, which encourages unnecessary idling.
  • Consider purchasing hybrid electric vehicles, which limit idling at traffic stops.

Heavy Duty Vehicle Owners:

  • Develop an internal company policy to reduce unnecessary idling.
  • Host an Idle Reduction workshop.
  • Post signs to remind employees not to idle.
  • Offer rewards to employees for idle reduction efforts.
  • Install telematics in your vehicles. This technology enables the monitoring of vehicles’ idling times. Telematics can tell you how well you are doing on increasing your fuel economy, where the vehicle is, how fast it is travelling and a number of other metrics.
  • Use alternative power sources and auxiliary power systems which can provide power for air conditioning, electronics and other devices.

Additional Resources

The Truth About Idling a Vehicle: How Turning Off Your Vehicle for 10 Seconds Can Save Millions (Sustainable America)
IdleBox Toolkit for Idle-Reduction Projects (United States Department of Energy)