The Class 8 truck gross vehicle weight rating (GVWR) is a vehicle with a GWVR exceeding 33000 lb (14969 kg). These include GMC C8500 trucks as well as most tractor trailer tractors, such as the Freightliner Cascadia for example, as well as single-unit dump trucks of a GVWR over 33,000 lb; such trucks typically have 3 or more axles. The typical 5-axle tractor-trailer combination, also called a “semi” or “18-wheeler”, is a Class 8 vehicle. Standard trailers vary in length from 8′ containers to 57′ van trailers, with the most common length being the 53′ trailer. Specialized trailers for oversized loads can be considerably longer. Commercial operation of a Class 8 vehicle in the United States requires either a Class-B CDL for non-combination vehicles, or a Class-A CDL for combination vehicles (tractor-trailers).