Evaluation of Freight Truck Anti-Idling Strategies for Reduction of Greenhouse Gas Emissions

Abstract

It is important to identify ways to reduce greenhouse gas (GHG) emissions in order to combat climate change. Freight trucks emit 5.5 percent of U.S. GHG emissions and one of key sources is long-haul sleeper cab truck engine idling. Some anti-idling strategies, such as auxiliary power unit (APU) and shore-power (SP), have been developed. The objective of this study is to assess the anti-idling techniques taking into account variability in of real-world; to develop a new methodology for measurement and evaluation of such techniques; and to obtain new data.

Anti-idling techniques as well as other strategies are assessed based on literature review. For robust assessment for specific situation, a methodology for quantifying real-world truck stop activities and fuel use and emission rates for the base engine and anti-idling techniques is developed. Quantified data are used to estimate avoided fuel use and emissions.

Thirty-three potential best practices for freight trucks are assessed. These practices could lead to 28 percent reduction of GHG emissions from 2003 to 2025. Some practices were estimated to have net cost savings concurrent with substantial GHG emission reductions. Sensitivity analysis was used to assess the effects of variability and uncertainty; for example, for APUs GHG emission reductions could vary from 0 to 5 percent. In order to more accurately assess the impact of APUs and SP, a detailed field study was executed.

A new methodology was developed to estimate real-world fuel use and emissions of twenty APU-equipped and SP-compatible trucks, divided equally between single drivers and team drivers. Single drivers had 1,520 hours of rest stops per year, which were comparable to the literature estimates but more than those for team drivers. APUs for single and team drivers accounted for 59 and 25 percent, respectively, of idling hours. For two trucks, APUs accounted for 85 percent of idling hours. Double-dipping, which is simultaneous usage of the base engine and APU and defeats the purpose of the APU, accounted for 0.1 to 29% of idling hours. SP usage was seldom observed.

Energy use rates are estimated based on electronic control unit data for truck engines and electrical load measurement for APU and SP. Engine emission factors were measured using a portable emission measurement system. Indirect emission factors from SP are based on utility grid emission factors. Fuel use rates are typically lowest in mild weather and highest in very hot or cold weather. Compared to the base engine, fuel use and CO2 emissions rates for the APU and SP are lower by 36 to 47 and 74 to 92 percent, respectively.

Taking into account the actual proportion of idling time for which the APU is used instead of the base engine, the avoided fuel use and CO2 emissions for single and team drivers are 22 and 5 percent, respectively. The projected avoided fuel use and emissions are lower than those from literature sources. The difference is because of relatively low base engine idling fuel use and emissions rates, relatively high APU fuel use and emissions rates, lower idle reduction activity, and double-dipping. Because of low APU utilization rates, 17 of the 20 trucks have no net cost savings for the APU. Aggressive usage of SP, or APUs where SP is not available, elimination of double-dipping and decreased base engine RPM should be encouraged in order to enhance fuel use and emission reductions during idling. There is the need for real-world data and consistent methodology in order to assess anti-idling strategies.