Biden Transportation Secretary Pete Buttigieg is weighing a vehicle miles tax (VMT) to fund the president's estimated $3 trillion infrastructure plan, which he plans to unveil next Friday.

A VMT would tax people per miles driven and presents an alternative to further raising the gas tax.

"We’re obviously going to have to come to more solutions if we’re going to preserve the user-paid principle," Buttigieg said Thursday of a potential VMT while testifying before the House Transportation and Infrastructure Committee.

His comment came in response to a question from Transportation and Infrastructure Committee Ranking Member Sam Graves, R-Mo., who has previously expressed support for the tax.

President Joe Biden and Transportation Secretary Pete Buttigieg, right, meet with Vice President Kamala Harris and members of the House of Representatives in the Oval Office of the White House in Washington, Thursday, March 4, 2021, on infrastructure

Graves said in January that relying on "declining fuel tax revenues for maintaining and improving our roads and bridges" was unsustainable in response to a study from the Washington State Transportation Commission that found a VMT would help the country avoid an infrastructure crisis as the gas tax declines and people move toward electric vehicles.

"The report clearly shows that transitioning to a VMT system is a more equitable way to charge drivers for the roads they use, and that we are in fact capable of beginning that transition now," Graves said at the time.

Buttigieg furthered the idea in a Friday interview with CBNC.

"I think that shows a lot of promise," the Transportation Secretary said of a mileage tax. "If we believe in that so-called user-pays principle. The idea that part of the way we pay for roads is you pay based on how much you drive. The gas tax used to be the obvious way to do it. It's not anymore."

Buttigieg said that while gas taxes have traditionally been part of the way the U.S. pays for the Highway Trust Fund, "we know that it can't be the answer forever because we're going to be using less and less gas."

"If there's a way to do it that doesn't increase the burden on the middle class, we can look at it," Buttigieg said of an increase in gas taxes, "but if we do, we've got to recognize that's still not going to be the long-term answer."