Skirting the issue

A FUNNY THING happened on the way to our story about advanced trailer technology this month. We realized that cutting-edge technology wasn't really the immediate issue.

The idea we had originally for the story you see on Page 25 was to provide a round-up of some of the advanced electronics that are available for use on trailers today. To a certain extent, we still did that. But trailer engineers that were interviewed for the story had more immediate concerns that they wanted to talk about. Their big issue: trailer skirts.

Ballyhooed (and forgotten) for decades, the idea of putting skirts on trailers has once again become fashionable in 2010. Not just fashionable, but de rigueur.

Skirts are one way to reduce aerodynamic drag. Historically, interest in aerodynamics tends to rise in conjunction with increases in fuel prices. The first OPEC oil embargo, which more than doubled fuel prices in the early 1970s, triggered an array of advancements in air-flow management technologies. Some of these concepts were ignored by the market, but others were readily adopted by fleets eager to save fuel at a time when diesel expenses were skyrocketing.

Almost overnight, square corners of van bodies and trailers disappeared, replaced by extruded aluminum corner posts and nose rails featuring radii that direct air around the van instead of tackling it head-on. Rounded corners were a low-cost upgrade to van design that provided immediate benefits.

The biggest cost of these aerodynamic upgrades to van bodies was not incurred by the customer but by the manufacturers of van body kits. The redesigned corners did not lend themselves to being produced as a kit, accelerating the decline of this common way of marketing van bodies. For customers, though, the cost/benefit was compelling. Van buyers were quick to embrace these and other devices like tractor-mounted fairings as OPEC forced fleets to give up bargain-basement fuel prices.

Engineers have looked at aerodynamic drag reduction from every angle — front, sides, rear, and floor. When it comes to reducing air drag, the front end of vans has provided engineers with plenty of low-hanging fruit. But with the California Air Resources Board (CARB) taking aim at van trailers, engineers are now looking a little higher up the tree — addressing more difficult areas such as the rear of the trailer and the underside, where the cost reductions for fleets are less pronounced.

Companies have addressed these areas off and on over the years by developing fairings for the rear of the trailer and skirts for the sides. Multiple sources, including CARB, indicate that skirts can reduce fuel consumption by approximately 5% under certain operating conditions. That can be a significant cost reduction for van fleets.

The skirts, of course, don't generate pure profit. In addition to their purchase price, practical considerations such as weight, ground clearance, and durability offset their cost savings.

But fleets operating in California no longer need to calculate a cost-benefit analysis for trailer skirts. CARB's “Heavy-Duty Vehicle Greenhouse Gas Emission Reduction Regulation,” changed all that when it took effect January 1.

The intent of the new CARB regulation is to reduce greenhouse gas emissions by improving the fuel efficiency of heavy-duty tractors that pull 53-foot or longer van trailers. To do so, CARB is mandating SmartWay certified or verified technologies such as low-rolling-resistance tires and aerodynamic devices — including trailer skirts. For details, please see our story on page 25.

While the mandate is a California law applicable only to trailers operating in California, the net effect of this regulation — like the state's recent regulation of transport refrigeration units — goes far beyond the borders of the Golden State. Large numbers of out-of-state carriers go in and out of California. They will need to wear skirts. And for those outside California who might be considering putting skirts on their trailers, here's another variable that can be thrown into the cost-benefit analysis. Money is available to help carriers buy skirts.

Interstate Distributor Company — ranked as the 12th largest truckload carrier in North America — has begun a major installation project at its maintenance facilities. The carrier is installing 2,058 Freight Wing Aeroflex side skirts on its fleet of 6,800 trailers, funded in part by an $875,972 grant from the Environmental Protection Agency through the Diesel Emissions Reduction Act (DERA).

Whether or not they make economic sense, we can expect to see a lot more skirts on trailers in the coming years. Cost effectiveness always takes a back seat when government grabs the steering wheel.

Agree or disagree? Make your voice heard by visiting and clicking on “Contact Us.”

Hide comments


  • Allowed HTML tags: <em> <strong> <blockquote> <br> <p>

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.