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Please note: This summary is provided to help you understand the regulations. Consult the references provided for links to the full text of the regulations.

Idling EmissionEngine Emissions (Truck, Idling)

Road Rail Air Water

This section covers regulations that limit truck engine idling. The focus here is on state and local laws and ordinances.

Who is covered by the regulations?

There are no federal regulations limiting truck idling. However, more than half of U.S. states and dozens of cities and counties have enacted idling laws or ordinances. Trucks operated in those states and local jurisdictions are covered by the regulations, including out-of-area vehicles that are in transit.

What is the purpose of the regulations?

For the states and local jurisdictions, reducing idling translates into substantial reductions of air pollutants. According to EPA studies, long duration truck idling annually consumes more than one billion gallons of diesel fuel at considerable costs to the trucking industry. As a result, truck idling annually emits more than 11 million tons of carbon dioxide and more than 180,000 tons of nitrogen oxides, as well as fine particulate matter and other harmful air toxics. For the trucking industry, reducing idling results in considerable fuel savings.


EPA has not promulgated, nor do they immediately plan to promulgate, any type of regulations regarding vehicle idling. Rather, EPA has decided that their role is that of a facilitator, to help create more consistent idling laws around the country. More consistent laws will achieve greater fuel savings and emissions reductions, and will make it easier for drivers to comply with them.

Anti-idling regulations and ordinances vary significantly among states and local jurisdictions. However, the overall objective is the same everywhere: to minimize unnecessary diesel engine emissions, especially in populated areas. Most frequently, idling laws limit the amount of time, in minutes, that a truck and operate its engine while not moving, with the most common idling limits being from 3 to 15 minutes. Most states and local laws have exemptions from idling standards that vary widely. These often include fixed exemptions such as truck size (less than 8,000 lbs. GVWR) or variable conditions such as traffic congestion, outside temperature (upper or lower limits), emergencies, while engaged in particulate matter trap regeneration, driver sleeping or resting in a berth, and windshield defrosting. Again, these are state- or local jurisdiction-specific rules and they vary widely, so be certain to know which standards you need to meet.

An excellent source of information on state and local idling regulations is the American Transportation Research Institute Compendium of Idling. ATRI is part of the American Trucking Associations (ATA) Federation. ATRI maintains a database of non-federal idling regulations. From their website, you can download a detailed summary of the rules and a convenient foldable cab card. ATRI frequently updates its summaries of state regulations, which covers more than 30 states. Although local rules are also covered by the ATRI resource, this information may be less comprehensive or current than their summaries of state regulations.

Compliance Options

In most states, anti-idling regulations apply to all semi-trucks. However, a number of states provide exemptions or partial exemptions from idling rules when certain types of equipment are used such as alternatively fueled vehicles and truck cabs displaying the California low NOx label (e.g., this applies in California, Pennsylvania, North Carolina, and West Virginia). In West Virginia, vehicles powered by clean diesel technology or biodiesel fuels are also exempt from idling rules. The American Transportation Research Institute provides a Compendium of Idling Regulations with access to specific regulations for each state.

In order to encourage the use of idling reduction devices in large trucks, the Energy Policy Act of 2005 allowed for a 400-pound weight exemption for the additional weight of idling reduction technology such as an auxiliary power unit (APU), which is a portable, truck-mounted system that can provide climate control and power for trucks without idling. States were given the discretion of adopting this exemption without being subjected to penalty. Most states now allow the 400-pound APU exemption. US DOT maintains information on the status of state-exemptions.

Best Practices

Under the SmartWay transport program, EPA has researched, developed, and encouraged the use of a wide variety of technology and non-technology strategies to reduce long-duration idling:

  • Behavioral Change achieved through informing the driver or operator about the impact of behavior on emissions, fuel consumption, and the potential health risks.

  • Technology Based Change that allows engine operators to refrain from long-duration idling of the main propulsion engine by using an alternative technology, including:

    • automatic engine shut down/start up,
    • direct fired heater,
    • diesel driven heating system,
    • auxiliary power units/generator sets, and
    • electrification of climate control and other power needs

EPA Resources

U.S. EPA -- Office of Transportation and Air Quality Contacts. This contact list contains the names and telephone numbers of U.S. EPA employees who can answer your specific regulatory questions regarding idling emissions.

Idle Reduction A Glance at Clean Freight Strategies (EPA 420-F-19-021). Reducing unnecessary truck idling can save fuel, reduce greenhouse gas emissions, cut air pollution, and save money. A typical long-haul combination truck that eliminates unnecessary idling could save over 900 gallons of fuel each year.

Driver Training A Glance at Clean Freight Strategies (EPA 420-F-19-019). Driver training programs can help trucking companies save fuel and reduce greenhouse gas emissions by increasing drivers’ skills, knowledge, and performance. A driver training program that improves fuel economy by 5 percent could save over $3,000 in fuel costs and eliminate 8 metric tons of greenhouse gas emissions per truck each year.

More Resources

American Transportation Research Institute Compendium of Idling Regulations. ATRI maintains a useful summary of state and local idling regulations, including links to statutes. ATRI also publishes a convenient summary card that is suitable for carrying in a truck cab.

Compilation of State, County, and Local Anti-Idling Regulations (EPA420-B-06-004, 2006). A detailed summary of state and local statues covering 30 states.

IdleBase, a database of idling regulations for all classes of on-road vehicles

Alternative Fuels Data Center idle reduction page

Emissions From Idling Heavy-Duty Trucks and Idling-Reduction Equipment (Technical Report)

Locations of Electrified Parking Spaces

Work Truck Idling Reduction (Fact Sheet)

Visit the Vehicle Technologies Office's Idle Reduction webpage for links to more idle reduction resources.