Idle Reduction Research and Development

The U.S. Department of Energy (DOE) is leading research and development on technologies that reduce the need for vehicle idling while maintaining or improving driver comfort. Some of these research efforts are described below.

Infrared photo of a truck cab

Comfort in the Cab

DOE leads idle reduction research projects, such as the Heavy-Duty Vehicle (HDV) Thermal Management program, also referred to as the CoolCab project, which uses infrared images to evaluate insulation and heat transfer in truck cabs. For more information, see Reducing Thermal Loads in Long-Haul Trucks.

Updated Comparison of Energy Use and Emissions of Idling Reduction Options for Heavy-Duty Diesel Trucks

Since researchers at Argonne National Laboratory completed their analysis of the full fuel-cycle effects of idle reduction technologies (work described in section below), emissions requirements for new trucks have become much more stringent. Analysis of preliminary data reveals that newer truck models at idle emit NOx at levels comparable to diesel auxiliary power units (APUs) and particulate matter (PM) at considerably reduced levels. To further reduce PM emissions, installing particulate filters on APUs, as required in California for APUs on 2007 and later model year trucks, is likely needed. Using fuel-fired heaters to provide cabin heat to resting truck drivers is still the option with the lowest emissions impact. All idling-reduction equipment reduces emissions compared to older trucks that do not meet new truck emission standards.

Estimating Energy Use and Emissions of Idling Reduction Options for Heavy-Duty Diesel Trucks

Pollution and energy analyses of different idle-reduction technologies are often limited to localized vehicle emissions, neglecting upstream energy use and regional emissions. Researchers at Argonne National Laboratory analyzed the full fuel-cycle effects of current idle reduction technologies. Researchers compared emissions, energy use, and proximity to urban populations for nine alternatives, including idling, electrified parking spaces, APUs, and several combinations of these. They compared effects for the United States and seven states. The research showed that it is important to consider the full-fuel-cycle impacts during any technology comparison, because upstream impacts can significantly alter the relative positions of the options.

Stop and Restart Effects on Vehicle Starting Systems

In 2015, Energetics Incorporated conducted a study for Argonne National Laboratory to investigate the concern some drivers have about starter motor and battery wear caused by turning a vehicle off and on frequently to reduce idling time. It concluded that, in general, drivers can save money by turning off the engine for short stops (<1 minute), such as at drive-throughs. When stopped in traffic, however, motorists should keep the engine on for safety reasons. For a typical driver, the wear on starting-system components resulting from additional daily start cycles will be negligible. For more information, see the report Stop and Restart Effects on Modern Vehicle Starting System Components—Longevity and Economic Factors.

Idling Versus Stopping and Restarting

Argonne National Laboratory researchers undertook a series of measurements to answer this question: "Considering both fuel use and emissions, how long can you idle in a queue, such as at a drive-through, before the impacts from idling are greater than they are for restarting?" They determined fuel use and carbon dioxide emissions are greater for idling longer than 10 seconds. For more information, see the fact sheet, Which Is Greener: Idle, or Stop and Restart?.

Medium-Duty Truck Cycle Project

To analyze the duty cycles of medium-duty trucks, including the extent of workday idling, researchers at Oak Ridge National Laboratory collected data on approximately 70 duty-cycle performance indicators from real-world vehicles in a variety of industries. The data acquisition systems actively captured details on fuel consumption, brake and tire performance, speed, and idling, as well as external conditions that impact duty cycle, such as precipitation, wind, road grade, and weight. Data collected are being used to support modeling and studies of fuel efficiency evaluation of tires, payload weight, speed, and driver style.

In-Cab Air Quality of Trucks Air-Conditioned at Electrified Truck Stops

Different methods of air conditioning a heavy-duty truck cab during rest stops produce different air quality outcomes inside the cab. Researchers at Oak Ridge National Laboratory compared the effects of using different air-conditioning methods at a Texas truck stop with electrified parking spaces. They found that using the electrified parking space power for air conditioning provided better in-cab air quality results for nitrogen oxide (NOx), carbon monoxide (CO), and particulate matter (PM) than did an idling vehicle. Using power from auxiliary power units (APUs, which are small diesel engines mounted on the exterior of the cab) for air conditioning also emitted lower levels of NOx, CO, PM, and total hydrocarbons than did idling vehicles. The study did not consider emissions produced by generating the electricity that powered the electrified parking spaces, since those occur in a different location.

Heavy-Duty Vehicle Thermal Management Research

Climate control is the primary reason truck drivers keep their engines running during rest periods. In warm weather, engine idling powers the air conditioner to offset heat from the sun and from the truck's engine and exhaust. In cold weather, idling heats the cab, protecting the driver from low outside air temperatures. Truckers experience a wide range of hot and cold conditions throughout their day and year. Some idle reduction systems introduced in recent years have lacked the capacity to maintain driver comfort under these varying thermal conditions. DOE and the National Renewable Energy Laboratory (NREL) initiated the Heavy-Duty Vehicle (HDV) Thermal Management program, also referred to as the CoolCab project, to improve the effectiveness of idle reduction systems.

The HDV thermal management program partnered with companies such as Schneider National, Volvo, and International Truck and Engine Corporation to quantify truck thermal loads, identify areas for improved thermal management, and evaluate thermal management technologies. An evaluation of the thermal load reduction benefits of privacy curtains and window coverings is detailed in the paper Thermal Load Reduction of Truck Tractor Sleeper Cabins. Ongoing HDV thermal management program work includes developing computer models of truck cab heat transfer and climate control and working with truck and idle reduction technology manufacturers to define idle reduction system requirements.

Idle Reduction Technology Demonstrations

DOE initiated a study of diesel truck engine idle-reduction technologies in 2002 through the Advanced Vehicle Testing Activity (AVTA). The study identified several barriers to widespread use of existing idle-reduction technologies, including initial cost, driver education and receptiveness, reliability, and maintenance considerations. The study results were used to develop a plan to implement idle-reduction technologies. As part of this study, AVTA sponsored four idle-reduction demonstration projects, which consisted of teams of a truck fleet, truck manufacturer, and idle-reduction technology manufacturer. See the project details and results in the 2007-2008 Final Status Report.

Other Government-Sponsored Idle Reduction Activities

The U.S. Environmental Protection Agency's (EPA's) SmartWay Transport Partnership sponsors idle reduction projects. EPA's Clean School Bus USA program pursues efforts to reduce children's exposure to diesel exhaust caused by school buses. DOE's Clean Cities Program lists funding sources for transportation projects, including idle reduction. The newsletter, National Idling Reduction Network News, is also an excellent source of information on idle reduction developments and funding opportunities.