An aerodynamic device used on tractor-trailer trucks. A spoiler is located on the roof of the tractor which deflects air from buffeting the trailer. Truck roof spoilers increase the top speed of the truck, save diesel fuel, and protect the refrigerator coils of refrigerated trailers from rocks that blow off of dump trucks.
The top speed of this Kenworth is 117 miles per hour, the same truck without the Spoiler only goes 113 MPH. By the end of the day I'm 64 miles ahead, because I have a Spoiler.