We Can Do Better Than Six Miles Per Gallon: Redesigning America's Truck Fleet

America's trucks burn an enormous percentage of our total fuel, but their efficiency hasn't improved in years. But new, simple additions to a truck's body can have impressive effects on fuel economy.

Walmart-truck

Trucks are miserable when it comes to gas mileage. America's 2.2 million freight trucks get about six miles per gallon on average, usually with cargo. And they aren't getting much better. While the gas mileage of cars is exploding, between 1990 and 2006, the average fuel economy of the U.S. truck fleet went from just under six mpg to... a bit more under six mpg in 2009, the Department of Transportation reported in 2009.

Since trucks burn significant fraction of the fuel used in the U.S. each year (Ed: we've fixed these numbers to reflect that trucks use diesel, not gas), even small improvements can have a major impact. But it's not as if truck manufactures have been sitting on their hands for the last two decades; they're just already done a lot to get that number up to six mpg. Truck designs were given a full aerodynamic makeover years ago which improved fuel economy by more than 15% compared to their 1980s predecessors.

Yet the combination of trailer and truck remains a problem. "Trailer aerodynamic improvements are much less developed," the 2009 DOT study reported."There is little interaction between tractor and trailer manufacturers, and as a result, there has been no effort to treat tractor-trailer aerodynamics as an integrated whole.”

A rectangular metal box, it turns out, may be the worst possible shape to haul down the highway at high speeds. It's a fashion show of new forms on the road: trailer skirts, trailer tails, and "SuperSingles" all designed to reduce the wind resistance sucking the efficiency out of America's freight shipping fleet.

The top three trailer makers, Wabash, Utility, and Great Dane, now provide trailer side skirts--panels along the bottom of the trailer which reduce wind resistance and improve mileage, like those on the Walmart truck pictured here--as factory installed options. ATDyanmics manufactures the TrailerTail, which smoothes out the airflow around the back of the trailers, and they've reportedly sold about 5,000 (Ed: This number has been corrected from 100,000) in the last 12 months alone.

"There is no more low hanging fruit left for fuel savings in the tractor or cabin, other than that of driver habits," wrote Babur Ozden, chief operating officer of ATDynamics which makes trailer aerodynamic devices, by email. "Getting another 1% fuel efficiency from the tractor is same as getting 5% from the trailer."

Ozden sees most of the trucking fleet, eventually, adopting the new technology. New durable materials, state and federal mandates, and a new generation of drivers and fleet owners interested in every possible competitive advantage, both financial and environmental, just makes business sense.

Of course, word of mouth doesn't hurt as well. "As more of and more of these trailers with skirts and now tails seen on the roads, other fleets get curious, interested, and place their initial orders for pilots," wrote Ozden. "From there, they go to fleet-wide adoptions."

[Image: Walmart's Flickr stream]

Reach Michael J. Coren via Twitter or email.

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2 Comments

  • Ryan Barnett

    Babur Ozden's quote of "There is no more low hanging
    fruit left for fuel savings in the tractor or cabin, other than that of driver
    habits" nails it on the head. 

     

    I work at a company, Xata Corporation, which helps fleets
    get the most out of their trucks through measuring and monitoring truck and
    driver performance.  We have seen fleets
    go from sub 5MPG to over 7MPG with the proper training, coaching, and inspection.   Things like shutting off the truck at idle,
    using the proper torque bands when shifting, reducing hard brake events, and not
    speeding are controllable items for a fleet. 
     When diesel is at $3.80 -
    $4.00/gallon, and you are traveling 25M miles a year, every 10th
    helps.

    Our clients have aggressive fuel economy goals and are
    actively looking at anything and everything that will get more out of the truck
    without compromising safety.  It’s
    exciting to see the use of technologies like telematics play a role in those
    gains. 

  • dinkster

    Commercial trucks run off of diesel, not gasoline. Diesel is already pretty efficient, around 45%. You mention "gas" and gasoline, but not diesel. The efficiency should include a function of weight, not just distance. Towing 90000 lbs at 5 mpg is a lot more efficient then pulling 3000 lbs at 25 mpg (typical car with passengers). Go to page nine of the report you sourced. Notice the units are in ton-miles/gallon. Trains do this even better, and they aren't aerodynamic at all. Any aerodynamic design you do to the trailer would be null if it came at the cost of reducing capacity. As you stated, third parties have already developed drag reducing skirts.