WASHINGTON, D.C. – Several major truck makers came together to conduct a two-year study that shows Class 8 trucks can reduce their fuel consumption by more than 10% by employing aerodynamic improvements to the tractor-trailer combination.

Gap enclosures, side skirts, boat tails and aerodynamic side mirror designs can combine to deliver an industry-wide fuel savings of a billion gallons per year in the US, announced the US Department of Energy, which sponsored the study carried out by the Truck Manufacturers Association.

The study found that every 2% reduction in drag results in a 1% improvement in fuel economy.

For its part, Freightliner participated in the study by offering the use of its state-of-the-art wind tunnel in Portland, Ore. to determine how new aerodynamic mirror designs can impact fuel consumption. The company found that not only does the shape of the mirror have an effect on fuel mileage, but so too does the placement of the mirrors.

“It’s not just the mirror shape, but the placement on the truck and even the shape of the truck in the vicinity of the mirror that affect the efficiency of the airflow,” the company announced when the results of the study were released in November.

Freightliner engineers discovered that mirror design alone can account for a fuel savings of 6% or more.

“Mirrors need to be integrated into the specific vehicle design because what works on one make or model may not perform the same on another,” said Scott Smith, executive engineer with Freightliner. “The real benefit from our study is that we have produced design guidelines that can be incorporated on any heavy-duty vehicle design to improve the airflow around mirrors regarding total vehicle aerodynamics.”

Wind tunnel and simulation testing allowed engineers to closely examine how water disperses on glass and mirror surfaces. Rainy and windy conditions were simulated so engineers could study how air and water flowed around the mirrors. The hope is that future designs will provide for improved forward and rearward visibility during inclement weather, the company reported.

International Truck and Engine also participated in the study, focusing on how aerodynamic drag could be reduced on Class 8 tractor-trailer combinations. Patrick Charbonneau, vice-president of government relations with International, pointed out half of the fuel consumed by tractor-trailers is spent overcoming aerodynamic drag at highway speeds.

“The industry must continue to squeeze as much performance as possible from these heavy trucks while also limiting the drain on natural resources and, ultimately, the cost to customers,” said Charbonneau.

International teamed up with Great Dane Trailers to develop a full-scale experimental aerodynamic trailer for Wal-Mart. The tractor-trailer gap, the trailer side and trailer wake were the focal points for International and Great Dane.

For starters, the front of the trailer was lowered by 8% to reduce drag. Loss of cargo space was minimized because the trailer floor was lowered and an adjustable suspension was installed so the trailer could be raised to match standard loading dock heights.

Side skirts were added to the trailer which deployed at speeds of 35 mph to reduce airflow underneath the trailer. The skirts would automatically raise at lower speeds to provide adequate ground clearance in loading yards.

Trailer wake was tackled by tapering the aft of the trailer to match optimal lengths and angles developed in the wind tunnel. The modifications resulted in a 7% improvement in highway fuel economy, Great Dane and International reported.

An experimental device that closes the gap between the truck and trailer has shown the ability to provide an additional 2% improvement in fuel mileage.

“Our goal is to design practical aerodynamic solutions which would lead to immediate fuel savings,” announced Charlie Fetz, vice-president of research and development with Great Dane. “Our effort with International shows significant progress towards this goal, incorporating important aerodynamic concepts into a very functional trailer.”

Not to be outdone, Mack and Volvo also took part in the study, experimenting with side skirts, gap enclosures and boat tails.

Mack officials say they realized an 8% improvement in fuel mileage by improving airflow around the tractor-trailer combination.

Like the International/Great Dane experiment, side skirts running nearly the entire length of the vehicle were found to prevent air from flowing underneath the trailer where it interferes with the axles and wheels.

The boat tail – a two-piece drag-reducing system affixed to the rear of the trailer – also helped improve airflow and gap enclosures prevented the front wall of the trailer from acting as a sail.

Mack officials announced the company is already exploring the possibility of producing an actual production gap enclosure based on the prototype used in the study.

Volvo officials were also on-hand at the demonstration in Washington to announce their research showed a 2.3% fuel economy improvement based on four modifications to a typical highway tractor-trailer combination.

Up front, it added a smooth underside to the truck itself which was essentially an extension of the bumper made from composite material. Meanwhile, a deck enclosure consisting of a plate between the chassis rails between the back of the truck and the fifth wheel was installed.

On the trailer, Volvo installed an air deflector that wrapped around the front and sides of the trailer bogie. It served as a poor man’s version of full side skirts.

Finally, Volvo added roof and side fairing extenders which are already available to customers. These reduced the gap between the rear of the tractor and the front of the trailer.

The study confirmed there’s still plenty of room for improvement when it comes to tractor-trailer aerodynamics, but implementing some of the changes will radically change the appearance of tractor-trailers as we know them today.