Idle Reduction Research and Development

The U.S. Department of Energy (DOE) has long led 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, where researchers use analysis and modeling to assess the energy saving impact of advanced climate control materials and equipment on heavy-duty vehicles.

Idling Reduction for Long-Haul Trucks: An Economic Comparison of On-Board and Wayside Options

Researchers at Argonne National Laboratory considered the costs and return on investment (ROI) of idling reduction (IR) equipment for both truck owners and owners of electrified parking space (EPS) equipment (also known as truck stop electrification equipment). In the case of truck owners, the analysis examined key variables such as the number of idling hours to be displaced (generally 1,000 to 2,000 hours per year) and the price of fuel ($0 per gallon to $5 per gallon). Owners agree that the ideal IR option would provide complete services in varied climates and locations, while offering the best ROI for trucks that log many idling hours. For trucks that require fewer idling hours, options with a fixed cost per hour (e.g., EPS) were most attractive. EPS, however, is particularly cost effective for trucks on prescribed routes with a need for regular, extended stops at terminals.

The analysis showed that for high idlers (about 2,000 hours per year), all idling reduction options save money over 5 years when fuel costs more than $2 per gallon. For low idlers (about 1,000 hours per year), the fuel-cost crossover point is higher. In some cases, payback may take more than 5 years.

For trucks requiring bunk heat, a simple heater (plug-in or diesel-powered) is almost always the most cost-effective way to provide heat, even if the truck is equipped with an auxiliary power unit (APU) or is parked at a single-system EPS location. For trucks requiring bunk air-conditioning, the use of a single-system EPS is the most cost effective option for those logging fewer idling hours. Even for trucks with higher idling hours, the cost of an EPS may be about the same as using on-board air conditioning. Determining the optimal IR equipment depends on the amount of idling to be displaced, geographical location, seasonal factors, and the availability of EPS.

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 the following section), 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 is likely needed (as required in California for APUs on 2007 and later model year trucks). When resting drivers need only heat, the use of fuel-fired heaters is the most cost-effective option and the one with the lowest emissions impact. All idle-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 local vehicle emissions, but it’s also important to consider upstream energy use and regional emissions. Researchers at Argonne National Laboratory analyzed the full fuel-cycle effects of idle-reduction technologies. They compared emissions, energy use, and proximity to urban populations for nine alternatives, including idling, electrified parking spaces, APUs, and several combinations of these. The researchers compared effects for the United States overall and seven individual states. The research showed that it is important to consider the full fuel-cycle impacts in 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 starter motor and battery wear caused by turning a vehicle off and on frequently to reduce idling time. The study 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

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?.

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

Different methods of air conditioning a heavy-duty truck sleeper 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 idling the 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 allows the vehicle’s heater to run and thereby keeps the driver warm. Truckers experience a wide range of hot and cold conditions throughout the year (or even day). Not all idle reduction systems have the capacity to maintain driver comfort under widely varying thermal conditions. DOE and the National Renewable Energy Laboratory (NREL) initiated the Heavy-Duty Vehicle (HDV) Thermal Management program 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.

Other Idle Reduction Activities

The U.S. Environmental Protection Agency's (EPA's) SmartWay Transport Partnership supports idle reduction projects. EPA's Clean School Bus USA program pursues efforts to reduce children's exposure to diesel exhaust caused by school buses.