Commercial trucks in the United States vary significantly in size and load-carrying capacity. These vehicles are classified by the United States Department of Transportation (DOT) based upon their gross vehicle weight rating (GVWR). The classes range from 1 to 8, with categories of light-duty (1–3), medium-duty (4–6), and heavy-duty (7–8). The 2007 statistics for combination trucks on the highway show that there are over 2 million trucks, each traveling an average of 65,000 mi per year (105,000 km per year) and consuming 12,800 gal (48,600 L) of fuel per year to give an average fuel economy of 5.1 mi/gal (46 L/100 km).