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.
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 of idling reduction 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 idle reduction option would provide complete services in varied climates and locations, while offering the best return on investment 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 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)—a small diesel engine mounted on the exterior of the cab—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 idle reduction 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 nitrogen oxide (NOx) at levels comparable to diesel 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
Emissions and energy analyses of idle reduction technologies often consider only local vehicle emissions, but it is important to also consider upstream energy use and regional emissions (e.g., from power plants). Researchers at Argonne National Laboratory analyzed the full fuel-cycle effects associated with the use 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 emissions positions of the options. For more information, see Emissions from Idling Heavy-Duty Trucks and Idling-Reduction Equipment.
Idling Versus Stopping and Restarting
Argonne researchers undertook a series of measurements to determine how long drivers can idle in a queue such as a drive-through before the impacts of idling are greater than they are for restarting the vehicle. The study found that fuel use and greenhouse gas emissions are greater for idling longer than 10 seconds. For more information, see the fact sheet, Which Is Greener: Idle, or Stop and Restart?.
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.
In-Cab Air Quality of Trucks Air Conditioned at Electrified Truck Stops
Sleeper-cab air quality depends on the method used to provide climate control. 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 electrified parking space power for air conditioning provided better in-cab air quality (e.g., reduced levels of NOx, carbon monoxide [CO], and PM) than did idling the truck. Using power from APUs for air conditioning also resulted in lower levels of NOx, CO, PM, and total hydrocarbons than did idling the trucks. The study did not consider emissions produced by generating the electricity that powered the electrified parking spaces, since those occur in a different location. More details can be found in the full paper, In-Cab Air Quality of Trucks Air Conditioned and Kept in Electrified Truck Stop.
Heavy-Duty Vehicle Thermal Management
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, keeping the driver warm. Truckers experience a wide range of temperature conditions throughout the year (or even day). Not all idle reduction systems have the capacity to maintain driver comfort under widely varying thermal conditions.
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.