U.S. Department of Energy - Energy Efficiency and Renewable Energy

Federal Energy Management Program

DOE and Leading Manufacturers Develop Aerodynamic Trucks

November 22, 2006

Freightliner employed wind tunnel tests to reduce the drag caused by side mirrors. Credit: Freightliner LLC

A two-year study by four leading U.S. manufacturers of heavy-duty "Class 8" trucks has yielded fuel economy improvements of as much as 9 percent. DOE teamed up with four members of the Truck Manufacturers Association to study fuel savings through improved aerodynamics in large tractor-trailers. The efforts, which were unveiled on November 14th, focused on devices to enclose the gap between tractors and trailers; side skirts to reduce airflow under the trailer in crosswinds; tapered backs for trailers; and side mirror designs with reduced drag.

Mack Trucks, Inc. turned its attention to the first three approaches and achieved an 8 percent improvement in fuel economy. International Truck and Engine Corporation teamed up with Great Dane Trailers to build an experimental trailer for Wal-Mart Stores Inc. The trailer is lower than normal and features a reduced frontal area, a tapered aft end, and side skirts that automatically deploy at 35 miles per hour and above. The trailer achieved a 7 percent fuel economy improvement on the highway, and International is currently testing trailer gap enclosures that could yield an additional 2 percent improvement. Volvo Trucks North America achieved a 2.3 percent improvement in fuel economy through a front bumper extension; extenders from the roof, sides, and bottom of the tractor to partially bridge the gap to the trailer; and an air deflector that wraps around the rear wheels and axles. Finally, Freightliner LLC worked on mirrors and mirror mounts, which can cause 6 percent of a truck's aerodynamic drag. See the press releases from Mack Trucks, International, Volvo Trucks, and Freightliner.

Class 8 trucks consume about 12 percent of the U.S. petroleum supply, and roughly half of that fuel consumption is used to overcome aerodynamic drag at highway speeds. If every tractor-trailer in the United States were able to boost its fuel economy by 10 percent, it would save nearly one billion gallons of fuel per year. The aerodynamic study is part of DOE's 21st Century Truck Partnership, which aims to dramatically reduce the dependence on imported oil to fuel U.S trucks and buses.