A lot of attention is paid to the fuel efficiency of passenger cars, but large commercial trucks need some improvements as well.
Semi trucks cover significantly more mileage than the average passenger car, and with much worse fuel economy.
As governments look more seriously at the problem of commercial-vehicle emissions, several companies have proposed radical redesigns of the modern truck to improve efficiency.
The latest such concept comes from Volvo Trucks, which sells large commercial vehicles under the same name and logo as Volvo Cars, but is actually an entirely separate entity.
Volvo claims its concept truck uses 30 percent less fuel than a comparable current truck, thanks to improvements in aerodynamics and a lower curb weight.
The concept is based on Volvo's FH 420 model, which uses a 12.9-liter inline 6-cylinder diesel engine.
Volvo modified both the tractor and trailer, claiming a 40-percent improvement in aerodynamic efficiency.
Some of the changes include chassis side skirts on the tractor, fairings covering all but the front set of wheels, and spoilers on the back of the trailer.
The truck rides on low-rolling resistance tires, and Volvo also replaced the side-view mirrors with cameras.
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Tesla and other carmakers have lobbied to make side-view cameras legal in the U.S. because of their aerodynamic benefits, but so far regulators haven't budged.
The Volvo concept truck's trailer is also 2.2 tons lighter than a conventional design, although Volvo did not specify how this was accomplished.
Work on the concept truck began in 2011, and the truck began testing last fall.
Volvo will continue working on it, aiming for a 50-percent reduction in fuel consumption.
The truck itself won't go into production, but Volvo says some of its aerodynamic elements are already being added to the trucks it actually sells.
More radical design changes may be needed on production trucks as the U.S. prepares to implement stricter fuel-economy standards.
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Regulators are expected to unveil new rules known as "Phase 2" this summer.
They follow "Phase 1" rules that cover trucks through model year 2018, and call for a 10- to 20-percent increase in fuel economy, depending on the class of vehicle.
Phase 2 rules are expected to cover model years 2019 through 2025, bringing commercial truck standards in line with Corporate Average Fuel Economy (CAFE) standards for cars.