A major federal program is on desperate financial footing. It’s too important and popular to cut drastically. But a combination of changing social patterns, technological innovation and bad policy design has thrown its accounts far out of balance, and it has begun to eat into general spending that should go to other national priorities.

The program is the federal Highway Trust Fund, which pays about half the yearly tab to build and maintain the nation’s roads, bridges and rails. At the moment, the loudest advocate for fixing it responsibly is a liberal Democrat, Rep. Earl Blumenauer of Oregon. This month, Blumenauer proposed two bills meant to refill the fund based on the simple, unassailable principle that those who use the roads should pay for them. The measures are backed by a broad coalition of business and labor groups, and they are sensible. That and $3.69 will buy you a gallon of gasoline.

Traditionally, Congress filled the fund with revenue from the federal gasoline tax. Because the amount of gasoline used generally corresponded with wear and tear of the roads, lawmakers saw a natural fit, and Republicans and Democrats repeatedly raised the tax as needs arose. Until 1993, that is — the last time Congress raised the 18.4 cent-per-gallon tax.

Since then, inflation has cut away about a third of the value of the revenue that the gas tax generates. Americans also are driving more fuel-efficient cars. The combination of congressional inaction and changing consumer habits has depleted the fund, which will be broke in a couple of years. Lawmakers will have to address that problem when they reauthorize transportation policy next year.

One of Blumenauer’s bills would raise the tax by a modest 15 cents over the next three years, and then index it to inflation, which Congress should have done in the first place. That would raise about $170 billion over a decade, he reckons. If anything, the increase should be higher. In addition to raising needed transportation revenue, a higher gas tax would combat many negative effects of gasoline consumption, such as greenhouse gas emissions and illness-inducing air pollution.

Still, in the era of the hybrid vehicle, a gas tax will become decreasingly useful. It remains the best existing template to shore up the trust fund. But some frequent drivers don’t buy much gas. So Blumenauer’s second bill would cautiously promote a better but more controversial way to pay for transportation infrastructure: taxes on the number of miles people drive.

A spokesman for the House Transportation Committee told us that lawmakers “will look at all options for addressing our surface transportation infrastructure” in the coming months. Blumenauer has provided two that should top their list.

Editorial by The Washington Post