Idling Facts

Idling is money out the tailpipe

Think about it - an idling vehicle actually gets negative MPG

FUEL WASTE: Whether a light-duty car, SUV or pickup, or commercial truck, needless idling burns hard earned dollars or company profits through the tailpipe. At $3.25/gal, an averaged sized car like a Toyota Camry can cost around $125 annually when idling excessively while parked. The average light-duty vehicle burns 0.375 gal/hr.; heavy-duty up to one gal/hr. According the the Office of Energy Efficiency & Renewable Energy, "Idling an Engine for as Little as 10 Seconds Will Use More Fuel than Stopping and Restarting the Vehicle" (up to 30 seconds for heavy-duty vehicles).


ENGINE WEAR: For every two minutes of idling, one mile could be traveled. "Ghost miles" accumulate on an idling engine. According to reliable sources, including the study: Oak Ridge National Laboratory Summary of OEM Idling Recommendations from Vehicle Owner’s Manuals, "Excessive idling can create engine wear and carbon soot buildup in the engine and components". This can lead to shortened life of motor oil, spark plugs and exhaust systems, plus decreased fuel mileage and the need to adhere to a "severe duty" maintenance schedule. For similar reasons, many owners manuals recommend avoiding excessive idling. For heavy-duty vehicle engine wear, read engine manufacturer's information on the Heavy-Duty page.

Idling is bad for air quality and health

Idling emissions can cause cancer, exacerbate heart conditions, and cause or exacerbate asthma

LIGHT-DUTY VEHICLES: Overall, the latest light-duty gasoline-powered vehicles have come a long way in reducing harmful exhaust chemicals, such as carbon monoxide, nitrogen oxide, sulfur dioxide, hydrocarbons, and benzene. But there are still factors where this exhaust is harmful to humans. A catalytic converter cannot render these chemical emissions less harmful until warmed up (a catalytic converter warms up faster when a vehicle is driven as opposed to idling). A caravan of idling vehicles, such as at a drive-thru or a school pickup queue greatly increase these emissions. Idling emissions are more toxic during hot and cold weather extremes. And carbon monoxide poisoning remains a threat for occupants of idling vehicles in enclosed spaces or in deep snow banks.


HEAVY-DUTY VEHICLES: Diesel engines in commercial trucks and school buses are durable and economical sources of power. The EPA states: "From 2007 to 2017, NOx emissions in the U.S. dropped by more than 40 percent. But there is more work to be done. Heavy-duty vehicles are the largest contributor to mobile source emissions of NOx and will be one of the largest mobile source contributors to ozone in 2025."


ADDITIONAL FACTS: Children and the elderly are especially vulnerable. California Air Resources Board Overview: Diesel Exhaust and Health.

Idling contributes to climate change

In California, parked idling annually emits roughly three million tons of CO2*

Greenhouse gas emissions from vehicles, chiefly carbon dioxideNASA: evidence that atmospheric CO2 has increased since the Industrial Revolution. (CO2), contribute to climate change. Overwhelming scientific evidence, including from the Executive Summary of the Fourth National Climate Assessment (NCA4), NASA, NOAA, the IPCC, even the Department of Defense, link climate change and global warming in part from human activities to the highest temperatures ever recorded on Earth, melting polar ice caps, rising sea levels, increasingly severe weather events, droughts, wildfires, flooding, and to the threat of many plant and animal species. And global warming caused by human emissions has most likely intensified the drought in California by 15 to 20 percent, scientists say.


According to the Air Resources Board, transportation amounts to 38% of California's greenhouse gas emissions, the highest economic sector in the state and higher than the national average of 26%.

Idling wastes energy

In California, parked idling annually burns roughly 300 million gallons of fuel*

Many of us are aware of conserving and saving energy, from turning off lights when leaving a room, to recycling. Turning off the keys of our parked vehicles is a simple energy conserving habit to get into.


Most gasoline and diesel fuels are derived from crude oil, a non-renewable resource. While the threat of depletion of oil has lessened ­— as North America has partially transitioned from exporting foreign "conventional" petroleum to the extraction of "unconventional" petroleum (primarily using the method of hydraulic fracturing or "fracking") — the critical challenge of the future remains to transition from fossil fuels to clean, renewable forms of energy. Why? Unconventional oil is much harder to extract making it more expensive, much dirtier, more environmentally harmful, and will increase the challenge of coming to grips with the global climate crisis. We still need oil, but there are opportunities to use less of it; to keep it in the ground. From extraction to emissions, oil is harmful to humans and our planet.

Idle Reduction Technologies for vehicle fleets from NACFE (North American Council for Freight Efficiency)




• The U.S. Dept. of Transportation - Office of Highway Policy Information - Motor Fuel Use - 2018: U.S. fuel consumption 180,737,076,000 gallons

• The U.S. Dept. of Energy originally stated in 2012 and maintains today: "Each year, U.S. passenger cars, light-duty trucks, medium-duty trucks, and heavy-duty vehicles consume more than 6 billion gallons of diesel fuel and gasoline—without even moving. Roughly half of that fuel is wasted by passenger vehicles."



•The U.S. Dept. of Transportation - Office of Highway Policy Information - Motor Fuel Use - 2018 - California fuel consumption 18,010,964,000 gallons

• Factor that decreases idling in California since 2012 U.S. DOE statement: as of the 3rd quarter of 2019, 7.9% of all vehicles in California are plug-in hybrid and electric. Additionally, hybrid sales are higher in CA than the rest of the country; this represents an approximately 10% idling decease in CA than nationally

• Factors that increase idling in California (and elsewhere) since 2012 U.S. DOE statement: nearly 5% increase in vehicle fuel use statewide; in-vehicle behaviors such as use of devices like smartphones; door-to-door delivery and ride-hailing services

• Putting this all together (in lieu of no far ranging studies on vehicle idling in California), based on U.S. overall transportation fuel consumption vs U.S. vehicle idling fuel consumption, it is estimated that all vehicles in California consume approximately 600 million gallons of fuel when idling annually. This results in six million tons of CO2 emitted by all idling vehicles in the state. This equates to idling in California being approximately 10% of idling nationally.


Studies show that about one-half of all idling occurs when parked (not in traffic).1, 2. Therefore, it is estimated all vehicles idling when parked in California consume 300 million gallons of fuel, resulting in three million tons of CO2 emissions. MOST OF THIS IDLING IS CONSIDERED UNNECESSARY.


IDLING PERCENTAGE: all vehicle idling (in traffic and when parked) is estimated to be 3.4% of all vehicle fuel consumption/emissions; vehicles idling when parked is estimated to be 1.7%.


1Vanderbilt University study: Costly myths: An analysis of idling beliefs and behavior in personal motor vehicles (p.4). "...the average American idles for roughly 16 min a day. Over 51%...can be accounted for by individuals idling while in traffic...the remaining 49%...results from idling to warm and while waiting, both of which are avoidable and, in many cases, unnecessary."

2University of Vermont study: Passenger vehicle idling in Vermont (p.25): "Discretionary idling is a large enough percent of all idling in Vermont (approximately half) to suggest policies to pursue behavior change over purely vehicle technologies which eliminate all idling emissions by turning off during travel and at stops."

Idling can be necessary

There are legitimate safety reasons that may necessitate idling

For light-duty vehicles in cold and hot weather extremes, idling can be necessary for several reasons. In colder weather, warm-up idling may be necessary for adequate windshield/window/outside mirror defogging/defrosting. This can be a visibility issue even at more than 50º in the morning. Below 10º, a warm up of 1 to 2 minutes is recommended to allow thickened motor oil to fully circulate in an engine.


It is strongly recommended to seek alternatives to being in a parked vehicle in weather extremes. But if there is no place else to go, for factors of safety and health, idling may have to occur (although it can in alternating on-off cycles). This is especially true if there is an elderly person, child, or pet in the vehicle. On a very hot day, especially if not parked in the shade, the vehicle will need to idle with windows closed and AC on.


For safety reasons, it is not recommended to turn off engines at stop lights; however, in prolonged situations such as at railroad crossings and road construction zones, it is recommended to turn off engines.


Other Idle Free Efforts


Spare the Air: Turn the Key – Be Idle Free! San Francisco Bay Area

Idle Free Bay Area (Spare the Air) - Oceanside: STOP IDLING page

Idle Free Oakland

Grades of Green - No Idle Zone Los Angeles South Bay area

U.S. Dept. of Energy Clean Cities coalitions: California has 13 Clean Cities implementing various degrees of idle

  reduction initiatives, as well as Clean Cities in other states. In general, Clean Cities offers their IdleBox Toolkit for

  idling reduction projects.



Keep it Clean. Be Idle Free. Washoe County, NV

Utah Clean Cities, Being Idle Free is Easy

Engines Off!, Denver CO

Kentuckiana Air Education (KAIRE) Idle Free, Louisville, KY

IdleFreePhilly, Philadelphia, PA (and suburbs)

Idle Free for Our Kids eLearning, Halifax, Nova Scotia

U.S. national: It's Your Turn - Turn It Off Sustainable America

U.S. Dept. of Energy: Idling Reduction for Personal Vehicles - EXCELLENT OVERALL GUIDE

U.S. Dept. of Energy Clean Cities: IdleBox Toolkit for Idling Reduction Projects

U.S. EPA Idle Free Schools for a Healthy School Environment