Taking these in turn, the key issues regarding the tax base are those vehicles that would be subject to the tax and those roads on which tax would be due. CBO focused on two illustrative possibilities: (1) all commercial trucks, defined as vehicles with six or more tires or a gross vehicle weight of at least 10,000 pounds, or only tractor-trailer trucks; and (2) all public roads, Interstate highways and arterial roads (non-local roads like highways and freeways), or Interstate highways only.
The overall rate obviously depends on how much revenue Congress wants to raise. But further considerations would allow the rate to differ in order to better approximate the wear and tear imposed on the transportation infrastructure. Specifically, the rate could vary by truck type or configuration (charge more for combination trucks), by weight or weight per axle, or by travel location (rural versus metropolitan).