Traffic near Woodstock, Va., in 2009. (Katherine Frey/The Washington Post)

Remember “Peak Car”? Vehicle miles traveled per capita hit an all-time high of just over 10,000 a year in 2004 — then declined for nine straight years, spawning a belief that the car-happy United States might have finally maxed out on driving. Baby boomers were retiring, millennials liked walkable cities, and more workers telecommuted. Futurists touted lower emissions of carbon dioxide and less valuable time wasted in traffic.

Well, as anyone who rode the interstates this summer can attest, cars are back. Vehicle miles traveled per capita rose in 2014, 2015 and in the first half of 2016, according to the Federal Highway Administration.

Cheap gas is one reason: A gallon of regular cost an average of $2.24 during the week ending Aug. 29 — about the same, in inflation-adjusted terms, as in 2004. A bigger factor, though, is the slow, steady economic recovery. As Eric Sundquist and Chris McCahill of the University of Wisconsin’s State Smart Transportation Initiative have shown, driving correlates even more strongly with gross domestic product growth than with gas prices.

And so we’re at a crossroads (sorry!). Driving is still well below its 2004 peak. But if trends continue, we’ll essentially repeat what happened between mid-1979 and mid-1984. Driving shrank sharply at the beginning of that half-decade, due to an oil price shock and recession — then recovered and went on to new heights as the economy rebounded. Or we can take steps to prevent that, preserving benefits of a less car-dependent culture that would otherwise be squandered.

Among those benefits is less wear and tear on our highways, which is to say: less need to spend billions of dollars on infrastructure, as both Hillary Clinton and Donald Trump are promising to do.

Indeed, the political stars seem to be aligning behind a major new federal infrastructure spending initiative in the next presidential term, especially because Congress could borrow some or all of the funds at record-low interest rates.

Many economists recommend doing just that, citing a 2014 International Monetary Fund study arguing that “productive and efficient” investment in infrastructure, financed at low interest rates, can pay for itself through enhanced economic growth.

The story of Peak Car is cause for caution, though. Note the IMF’s proviso — “productive and efficient.” It is, was and always will be devilishly hard to project the long-term payoff of large-scale infrastructure investment. (Bonded debt, by contrast, is pretty much inescapable.)

If you doubt it, take a walk along Washington’s muddy, long-defunct C&O Canal, whose backers thought it would revolutionize transportation in the 19th century — but failed to anticipate railroads.

Of course, it wouldn’t be rational to require cash up front for infrastructure, either. The trick is to limit the known risks of misinvestment, then devise equitable ways to share them, among current citizens and future ones.

The intellectual author of the Interstate Highway System, President Dwight D. Eisenhower, initially wanted it to be all toll roads, but that was politically impossible. He settled for the next-best thing: a dedicated trust fund (60 years old in 2016) supplied by excise taxes on gasoline and diesel. In a loose, good-enough-for-government-work sort of way, this established a link between how much drivers and truckers used the system — i.e., its value to society, now and in the future — and how those roads got paid for.

That link has been broken in recent years, by the legislated diversion of trust fund money to mass transit and the like and also — more importantly — by the failure of Congress to update fuel taxes. Last year, the fund nearly ran out of cash; Congress resorted to a gimmicky short-term fix that raided other government accounts.

The 18.4-cent-per-gallon gas tax was last raised in 1993; adjusted for inflation, that’s a 40 percent cut over 23 years. In other words, the U.S. government has been subsidizing highway use by charging drivers an ever-smaller percentage of what it costs to pound their SUVs over the asphalt, wearing it out.

Yes, driving declined for much of that time anyway. The point is how much more, and how much more lastingly, it might have dropped if gas taxes had just kept pace with inflation.

At least we could have had a closer fit between use of the roads and responsibility for maintaining them — and all the benefits, environmental, social and financial, that would have flowed from that.

For politicians, it’s axiomatic that raising gas taxes is electoral suicide. But is it? Eight states, mostly in the car-dependent South and Midwest, raised fuel taxes last year to pay for roads, and 98 percent of the legislators who voted for the hikes won their reelection primaries, according to a study by the American Road & Transportation Builders Association.

Maybe after years of low gas prices, some voters feel they can afford to chip in a bit more for highway maintenance. Maybe out there in the heartland, Eisenhower’s spirit lives on.

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