As a way to trim fuel costs, trucking companies routinely invest in specialized fairings, skirts, and gap reducers to improve aerodynamics. These items can boost fuel efficiency by 5 to 9 percent, saving thousands of dollars per year.

What they might not realize is that even the smallest details—like the trailer's mudflaps—can make a difference as well. One example is the "Eco Flaps" splashguard, a new type of aerodynamic mudflap that's included in the latest version of the U.S. Environmental Protection Agency (EPA)'s "SmartWay Verified List of Aerodynamic Devices."

The new flaps look nothing like the thick rubber mats that have hung off the back wheels of 18-wheelers for decades, bearing the image of a pistol-brandishing Yosemite Sam or a cartoonish female silhouette.

Rather, the new generation of splashguards, which were designed by Brenéwood, Tenn.-based Eco Flaps, are sleek slitted screens made of injection-molded nylon. The gaps allow wind and water to pass through the mudguard before being diverted to the pavement on the other side.

Their aerodynamic design qualifies the flaps for the EPA's 1-percent fuel savings category, although the manufacturer says the splashguards can improve miles per gallon by 3.5 percent, saving approximately 700 gallons of the 20,000 gallons a truck will use annually.