Walmart of Bentonville, USA; CC BY 2.0; Uploaded to Wikimedia Commons by Magnolia677 https://commons.wikimedia.org/wiki/File:Walmart%E2%80%99s_Grease_Fuel_Truck.jpg; Created 13 March 2009
Trailer sides skirts are aerodynamic devices formed from rigid sheets of one or more materials including metal, plastic or composite mounted along or slightly under each side of a trailer filling the gap between the front and rear wheels, and the trailer and ground, to reduce turbulence and streamline airflow passing over, around and under the trailer.