Wednesday, June 23, 2010

Clean Cities Technical Response Service (TRS) Question of the Month

Welcome to the June installment of the Clean Cities Technical Response Service (TRS) Question of the Month.

Question of the Month: Why is idle reduction important? What are the alternatives to letting a vehicle idle?

Answer: Idling vehicles in the United States use upwards of one billion gallons of fuel and emit large quantities of air pollution and greenhouse gases unnecessarily each year. On average, a heavy-duty vehicle consumes fuel at the rate of 0.8-1.0 gallon/hour at idle. A typical light-duty vehicle consumes 0.5 gallons/hour while idling. These rates are based on a number of data sources, including reports from the U.S. Environmental Protection Agency (EPA) and Argonne National Laboratory. The actual rates may be more or less depending on the type of vehicle and engine. Using EPA’s assumptions for carbon dioxide (CO2) emissions from each gallon of diesel and gasoline burned (
• The average diesel-powered heavy-duty vehicle emits between 17.8 and 22.2 pounds of CO2/hour while idling.
• The average gasoline powered light-duty vehicle emits approximately 9.7 pounds of CO2/hour while idling.

One of the most common myths about engines, particularly diesel engines, is that they need to idle for several minutes or more to warm up prior to driving. While some diesel engines do need to warm up, most engine manufacturers recommend that newer engines need no more than three minutes of warm-up before driving; drivers should check their engine manufacturer’s recommendations and/or owner’s manual about guidelines for engine warm-up. See the Additional Resources section below for more idling information.

Idle Reduction Regulations
Many states and localities have enacted regulations that restrict drivers from idling for extended periods of time. Reference the Incentives & Laws database available via the Alternative Fuels & Advanced Vehicles Data Center (AFDC; for state-level idle reduction regulations. In addition, the American Transportation Research Institute maintains a compendium of state and local idle reduction restrictions (

Idle Reduction Technologies
Heavy-Duty Idle Reduction Technologies
EPA research shows that certain heavy-duty vehicle idle reduction technologies can reduce idling fuel consumption by up to 96% and nitrogen oxides (NOx) emissions by up to 99%. Available heavy-duty idle reduction technologies include:
• Auxiliary power units are portable, truck-mounted systems that can provide climate control and power for trucks without idling. These systems generally consist of a small internal combustion engine equipped with a generator and heat-recovery system.
• Automatic engine stop-start controls automatically turn the engine on when the sleeper cab temperature is too warm or cold.
• Cab and block heaters are fuel-fired heaters that provide heat to the cab and the engine block.
• Truck stop electrification is an alternative to onboard idle reduction equipment that allows truckers to “plug in” vehicles to operate necessary systems (e.g., air conditioning, electrical appliances) during required resting periods at truck stops without idling.

Light- and Medium-Duty Idle Reduction Technologies
Light- and medium-duty vehicles, including personal and commercial vehicles, use significant amounts of fuel to idle. The following technologies are available for light- and medium-duty vehicles:
• Coolant heaters draw gasoline or diesel from the fuel tank to heat the vehicle's coolant and pump the heated coolant through the engine, radiator, and heater box.
• Air heaters operate on engine fuel, but are separate, self-contained units that directly blow hot air into the interior of a vehicle.
• Energy recovery systems use the vehicle's heat-transfer system much like a coolant heater but without a separate heater. A very small (1/10 amp) electric pump is connected to the water line, which keeps the vehicle's cooling system and heater operating after the engine is turned off, using engine heat that would otherwise dissipate for energy.

Driver Behavior
In addition to the technologies mentioned above, all drivers, regardless of the type of vehicle being driven, can use the following techniques to reduce idling:
• Turn off the engine when parked or stopped for more than a minute.
• Encourage local schools to enforce a no-idle zone for school buses and personal vehicles.
• Consider the purchase of hybrid electric vehicles, which limit idling at traffic stops.
• Avoid using a remote vehicle starter, which encourages unnecessary idling.
• Avoid drive-thrus: park the car and walk inside instead.

Additional Resources
For additional information about idling, see the following resources:
• AFDC - Idle Reduction (
• EPA - What You Should Know About Truck Engine Idling (
• EPA National Idle Reduction Campaign (
• EPA SmartWay Transport Partnership - Idling Reduction (
• Idling Reduction Network News (

As always, please contact the TRS with other questions, or if you have suggestions for additional resources or a future Question of the Month.

Clean Cities Technical Response Service Team

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