Out of any vehicle on the interstate today, few could be more aerodynamically challenged than the common semi-trailer truck, the most common vehicle in the commercial trucking industry.
With a boxy shape, massive proportions, and plenty of room for airflow beneath the trailer, a big rig creates heavy air resistance that flows around and under the truck, generating drag on the back end of the vehicle. The extra work through which this puts the truck's machinery reduces its fuel economy, adding a hefty chunk to what's already a costly bill for a year's fuel.