A number of senators and some lobbyists have advocated increasing the gas tax as the most expeditious means of bolstering the flagging Highway Trust Fund. (Rick Bowmer/AP)

There are times when a bit of research yields a telling statistic, and this is one of them: Gasoline consumption fell by 11 percent over a decade during which the U.S. population grew by 8 percent.

That fact, revealed in the latest paper by Michael Sivak at the University of Michigan Transportation Research Institute, and several other of his facts provide a framework ripe for extrapolation.

If the trend toward fuel efficiency continues — and there are more reasons to think that it will than that it won’t — that may speed movement toward energy independence and lower pollution.

But with Congress facing a May 31 deadline to find more money to fund transportation, bumping up the federal tax on gasoline, now 18.4 cents per gallon, seems like a bad bet to ensure a long-term flow of cash.

A number of senators and some lobbyists, including AAA and the influential U.S. Chamber of Commerce, have advocated increasing the fuel tax as the most expeditious means of bolstering the flagging Highway Trust Fund, the destination for gas tax revenue and the source of federal transportation funding.

In the House, however, the reception for a gas tax hike ranges from tepid to frigid.

The most likely funding scenario with time running out is a short-term extension of current funding and a move toward repatriation of $2 trillion in corporate earnings stashed overseas. Luring that money home with tax breaks, lawmakers could then dedicate the revenue to transportation under several proposals afloat in Congress.

Even with a bipartisan embrace, repatriation as a quick source of cash may run afoul of those on Capitol Hill who insist it must be part of a larger, more complex reform of corporate taxation that would take longer to go into effect.

Taking longer is a revenue-painful option. When Congress last summer extended current funding until the end of May, it had to reach into the general fund for $10.8 billion that the trust fund could not provide.

Sivak provides a sobering analysis for those who hold hope that the gas tax might provide a revenue solution. It is an apolitical, fact-based examination, the latest in a multiyear series he has produced on driving and fuel consumption in the United States.

In the paper he released this month and in his earlier work, Sivak presents data that show an 11 percent drop in fuel consumption by light-duty vehicles — cars, SUVs and pickup trucks — from 2004 to 2013.

With statistical support, he says that there is more to the drop than simply the fact that there are more fuel-efficient vehicles on the roads.

He says there are fewer cars on the road than there were in 2008, that they are not being driven as far as they were in 2006, and that there are fewer cars per household than there were in 2006.

Sivak concluded that the data probably reflects “fundamental, noneconomic changes in society.”

“There is no evidence in the 2013 data that the recent reductions in rates were temporary,” he wrote.