WASHINGTON — The roots of today’s transportation funding dilemma date to the 1990s, when the economy was roaring, deficits were shrinking and gas tax revenue was reliably increasing every year, thanks in part to two gas tax increases during that decade.

The Highway Trust Fund was flush with cash, prompting lawmakers to increase spending in the 1991 and 1998 highway reauthorization bills. By fiscal 2001, however, spending had overtaken revenue and the fund’s balance started to shrink.

In 2005, a six-year highway bill maintained high levels of spending but did nothing to boost revenue, depleting the fund’s balance even further.

Between 2000 and 2007, the federal government burned through $14.4 billion from the trust fund’s balance. Eventually, the Bush administration had to ask Congress for an emergency bailout of $7 billion in 2008, the first of many.

Lawmakers “assumed that as gas tax revenues fell and as the Highway Trust Fund began moving toward the situation it faced in 2008, Congress would enact a gas tax increase, and of course it didn’t,” says Emil Frankel, a top Department of Transportation official in the George W. Bush administration.

The most recent highway bill, enacted in 2012, covered only two years and, for the first time in recent history, called for reducing the amount of money allocated to states for transportation projects.

That legislation has been extended but its authorization runs out at the end of May.

To complicate matters, it’s becoming increasingly clear that no amount of economic recovery will save the Highway Trust Fund.

Since its inception in 1956, the fund has relied largely on gas tax revenue. In the past, that was a reliable way to raise steadily increasing amounts of money.

Not anymore. The rise of hybrid vehicles and the Obama administration’s boost in fuel efficiency standards are holding back gasoline consumption, even though Americans are starting to drive more miles as the recovery takes hold.

In the coming years, gas tax revenues to the trust fund and spending will diverge, for the first time in the fund’s history. The Congressional Budget Office forecasts revenues will stall at around $40 billion a year for the next decade, while spending rises to $60 billion annually by 2025.

That means that lawmakers are either going to have to increase the gas tax for the first time since 1993 or come up with an entirely new way of paying for projects.

“The funding base has gotten out of sync with the funding demand,” says Donald Kettl, a public policy professor at the University of Maryland.

Transportation Secretary Anthony Foxx made that point repeatedly during a February visit to Congress.

“We should look at the system as we have it today and look at the funding challenges we have as an opportunity to think differently about not only how we fund it but what those funds actually get put toward,” he said.