Back in 1956, the federal government created the Highway Trust Fund. The basic idea was to use money collected from the federal tax on gasoline and diesel fuel to pay for construction and maintenance of federal highways. When the interstate highway system was completed back in the early 1990s, this obviously meant that less funding was needed. But the Congressional Budget Office projects maintenance spending for the federal highways at nearly $60 billion in the next few years, gradually rising over time. Meanwhile, fuel-tax revenues for the Highway Trust Fund are below $40 billion per year, and gradually falling over time with the rise of higher-mileage cars in the short-run, and also the rise of electric vehicles in the long run.
Of course, one option is just to fill the gap with general tax revenues, which is what we have in fact been doing in the last few decades. But if we would prefer to return to something closer to the earlier “user pays” approach, in which the main users of highways pay for their maintenance, then there is an argument, laid out by Michael E. Gorman, for “A Vehicle Mileage Tax for Heavy Trucks?” (Regulation magazine, Winter 2024-2025).
Why a mileage tax just on heavy trucks?
1) Heavy trucks do most of the damage to highways. Gorman discusses the evidence form the most recent Federal Highway Administration report.
A 2000 Federal Highway Administration (FHWA) report estimated that for each mile traveled, combination trucks (a tractor with one or more trailers) imposed a road repair cost average of 66¢ a mile (FHWA 2000). For all trucks, the estimated road maintenance cost per mile traveled ranged from 4¢ to 40¢ (in 2024 dollars) depending on the weight of the load. According to Bureau of Transportation Statistics (BTS) calculations, trucks today effectively pay 4¢ per mile (calculated at 24.4¢ per gallon and 6.1 miles per gallon average).
In short, the fuel taxes paid by trucks don’t come close to covering the highway maintenance costs that they impose. As Gorman points out, heavy trucks also have additional social from their contributions to air pollution and traffic congestion.
2) There are relatively few heavy trucks compared to passenger vehicles, and the truck already need to keep track of their mileage for business and regulatory purposes. Indeed, most trucks already have transponders for when they are passing through toll plazas and weighing stations. Thus, the practical task of applying a mileage tax to heavy trucks is relatively straightforward. Several states have been conducting pilot programs with a vehicle-mileage tax for trucks–New York, New Mexico, Kentucky, and Oregon–with the general pattern that “[w]hile the initial set-up costs were significant, the ongoing administrative costs were slight.”
3) A worry about applying a mileage tax to personal vehicles is that it potentially invades the privacy of users. This privacy argument carries little or no weight when applied to the business of heavy trucks.
Of course, the trucking industry hates this idea. At present, heavy trucks receive an implicit subsity, and a vehicle-mileage tax would raiase the cost of trucking to reflect the actual maintenance costs. It would have other effects as well. For example, it would probably would cause a certain amount of freight to shift to rail, but since the environmental and traffic congestion costs of rail are lower, this shift should be viewed as a social benefit. (If the US was able to reform the Jones Act rules that have raised the cost of ocean-shipping between US ports, then a certain amount of freight could also move across water, rather than over land.)
One way or another, the costs of road maintenance will be paid, either out of general revenues, or if the maintenance is postponed, it will be paid out of additional wear-and-tear on vehicles. A vehicle-mileage tax on heavy trucks is a better choice.