Facing large debts that will be partly of his own making, thanks to last week’s spending bill, President Trump must now find sources of funding for his next big priority: the infrastructure bill he has promised.

[Republicans consider the unthinkable: A gas tax increase to pay for infrastructure]

The loudest voices so far among big business and the environmental lobby have argued for more than doubling the federal gas tax. But on Tuesday, Transportation Secretary Elaine Chao expressed skepticism, stating that the tax has a “very regressive impact” on low-income citizens and that a gas tax hike “is not ideal.”

Chao is right about this, but there’s a stronger argument still against relying on a massive gas tax increase to fund everything. Namely, such a tax hike would amount to a further huge subsidy for a big business.

As the U.S. Government Accountability Office once described in a 1979 report on the then-still-new Interstate Highway System, the damage that vehicles do to road surfaces does not rise proportionally according to vehicle weight. Rather, it rises exponentially according to vehicle weight. So the operator of a fully loaded 80,000-pound tractor-trailer will pay perhaps only four times as much as you do in gas taxes, just because he gets worse gas mileage. But you would need to take the same trip in your one-ton car as many as 10,000 times in order to cause as much road damage as his truck causes to the same roads and bridges in a single go.

This is why the commercial trucking industry is so eager to fund infrastructure going forward by increasing the very tax that falls most disproportionately on the other users of the roads. They don't want new highways to be tolled, because they are the most likely to use tolled highways on a given day, and the tolls, which can be set by axle, will fall on them most heavily.

A fuel tax might sound great to someone whose only goal in life is to reduce carbon emissions, but there is no practical way to make a fuel tax discriminate between truck and car drivers, and between those who use highways every day and those who only drive on local roads. This means that the gas tax inevitably forces the average motorist who drives his car or SUV down the street to work every day to pay an unfair share of the cost of fixing interstate highways he might rarely or never use, nearly all damage to which is done by heavy commercial trucking.

That average motorist should of course pay his fair share for federally funded infrastructure — after all, many motorists do use highways. But it simply isn’t fair to rely on the gas tax as the big infrastructure funding solution for the future. It would be much fairer, and just as feasible given current technology, to let the states toll many more highways and to lean on higher truck tolls especially.

Commercial trucking is vital to America’s economy. But that doesn’t mean the industry should be able to impose its costs to taxpayers. The cost of roads should be borne as much as possible by those who use the roads most and do the most road damage and by the customers to whom they would have to pass the higher costs.