Truckers Don Their Skirts

Those cool-looking aerodynamic cowlings atop the cabs of 18-wheelers may soon have company – aerodynamic skirts along the base of the trailers and odd-shaped "boat tails" for a trailer's stern.

It's all in the name of improving fuel economy – and reducing greenhouse gases and other emissions – by smoothing air currents along and behind a trailer.

Aerospace engineers at Delft Technical University in the Netherlands conducted wind-tunnel tests on the skirts and estimated that they would reduce wind resistance by 14 to 18 percent. That translated into a 7 to 9 percent increase in fuel economy.

Field tests on trucks operated by one of the country's largest freight haulers showed that the skirts improved fuel economy by 10 percent. And while the tails haven't been road-tested yet, wind-tunnel experiments pointed to additional gains. Working in tandem, these aerodynamic additions could boost fuel economy by up to 15 percent.

The team, led by Michel van Tooren, notes that since many trucks use skirts now to prevent other vehicles from "under-running" the trailers in an accident, it would be fairly straightforward to replace many existing skirts with more aerodynamic models. They could pay for themselves within two years, the team estimates.