The per-mile rate for road usage charge shown on your Driving Report is based on the amount the average car currently pays in gasoline taxes per mile driven. Your Driving Report includes two components: the state gas tax and the county gas tax for the county where your vehicle is registered. The state gas tax is 16 cents per gallon, which works out to about 0.8 cents per mile for the average car. County gas taxes range from 16.5 cents per gallon to 28 cents per gallon, or 0.8 to 1.1 cents per mile.