Photograph by Chip Somodevilla/Getty

Senate Majority Leader Mitch McConnell is a conservative Republican. Senator Barbara Boxer is a liberal Democrat. So the fact that they’ve worked together to come up with a plan to fund highway spending for the next three years might seem like a good thing, a rare moment of bipartisanship in a Congress riven by ideological hostility. And, in fact, you could see the thousand-page bill they’ve produced as, in the words of the Times, “real progress,” except for one thing: their complicated, jury-rigged plan is only necessary because of the continued refusal by Congress to embrace the obvious, economically sensible solution to highway funding, namely raising the gas tax.

The federal gas tax is, as it should be, a key source of funding for highway spending. Currently, the tax is 18.4 cents per gallon. The problem is that it has been 18.4 cents per gallon since 1993. And since the cost of building and, above all, repairing roads has risen substantially in the past twenty-two years, because of inflation and because the federal highway system is deteriorating, while the revenue from the gas tax hasn’t risen nearly as much, Congress has had to find other ways to make up the difference. In recent times, those fixes have all been short term, which is why the Boxer-McConnell plan, which would fund spending for three entire years, seems to some like a real improvement.

The problem is that the funding mechanisms the plan relies on are as gimmicky and haphazard as ever. The bill would raise money by, among other things, lowering the dividend rate paid to banks in the Federal Reserve system, raising certain customs fees, increasing collection rates on unpaid taxes, and selling off a hundred and one million barrels of oil from the country’s Strategic Petroleum Reserve. Some of these may, on their own, be reasonable ideas—although, if you’re going to have a Strategic Petroleum Reserve, you should probably only sell oil from it for strategic reasons, not just because you want to raise some cash. But they are, for the most part, stopgap measures, meaning that Congress won’t be able to rely on them the next time around. And, from an economic perspective, paying for operating expenses by selling off assets is not a good way to manage your money.

What’s especially infuriating about the bill is that we already have, in the gas tax, an ideal tool for raising money to pay for highway repairs. It’s a user tax: if you don’t drive you don’t pay it, and if you drive less it costs you less. It helps to correct, at least mildly, a clear market failure: people who drive don’t pay the full costs of the externalities they create, including the wear and tear they put on roads, the pollution they emit, and the congestion they help produce. And while certain taxes disincentivize, to some degree, things we like (such as work or investment), the gas tax, by raising the cost of driving, gets us less of things we don’t like (pollution, carbon emissions, and road wear). That’s why even conservative economists, like Gregory Mankiw, have been ardent advocates of gasoline taxes. This is also an excellent moment to raise the gas tax, since oil and gas prices are so much lower than they were, making any price increase at the pump more palatable to drivers.

Members of Congress have tried to get Washington to do the logical thing. Last year, Republican Senator Bob Corker and Democratic Senator Chris Murphy worked together on a bill that would have increased the gas tax by twelve cents over two years and then indexed it to inflation, in an attempt to insure that it kept pace with infrastructure needs. The plan wasn’t perfect (in order to make the hike palatable to conservatives, it made some temporary tax breaks permanent), but it was well considered, and would have made the value of today’s tax roughly equivalent to what it was in 1993. But the bill never even came up for a vote.

The fundamental problem, of course, is that raising taxes, no matter how economically sensible those taxes might be, is anathema to a huge swath of the Republican Party. (It’s hardly a coincidence that the last gas-tax increase came in 1993, just before the G.O.P.’s Contract with America transformed Congress.) And Republican resistance, in turn, makes it harder for Democrats to vote for tax increases, at least those that affect ordinary citizens, because they know that Republican challengers will use their votes against them.

Indeed, the refusal of Congress to raise the gas tax is the ultimate expression of how reflexive and irrational the resistance to taxes has become. Opposition to higher income taxes has some theoretical justification: higher marginal rates discourage people from working more and investing. Seen in one light, they’re a penalty for success. But no such argument exists against the gas tax: all it does, in essence, is ask drivers to pay for the roads they use. It’s not even fair to say that keeping this tax at its current level is a check on big government, since most federal highway spending now goes toward rebuilding and repairing roads—maintenance that even conservatives recognize we must do.

Highway revenue has to be raised somehow. Congress should show some political spine, discard the Rube Goldberg funding schemes, and stop treating all taxes as bad ones.