One of the immovable forces of Washington-area politics, cemented when Gerald Ford was president and Rod Stewart topped the Billboard charts, could be starting to budge.

At least that’s the view of the man Virginia Gov. Terry McAuliffe (D) sent to try to end the commonwealth’s decades-long political stalemate over Interstate 66.

As part of intricate and ongoing negotiations over the fate of the road and its surroundings, Arlington County politicians’ principled — or intransigent — opposition to widening the ­traffic-choked route to the nation’s capital has, in the word of Transportation Secretary Aubrey Layne, “softened.”

Layne said he believes that the broad framework of a deal has been struck: I-66 would be converted to a toll road inside the Capital Beltway, with carpoolers riding free. The tolls — tens of millions worth — would be channeled to just the types of Metro, bus, bike and pedestrian improvements that county officials have long argued are the best way to move growing numbers of people.

Then, after giving those ­changes a chance to work, state and local officials would analyze how the package of tolling, tighter carpool restrictions and transit improvements have affected congestion on I-66. Depending on what the numbers show, plans for expansion could then be considered, Layne said.

“That was spelled right out — consideration of future widening. It looks like some time in the year 2025, if not before then, based on traffic flow in the area,” Layne said. Before taking that up, though, Arlington wants to “explore every other alternative” and make sure their benefits have been “exhausted,” he added.

But make-or-break details, including the timing and precise triggers for when widening might proceed, are still a matter of deep dispute, and some areas that Layne and his team thought were settled aren’t, according to interviews with local officials. And the potential deal could easily drown in the same political swamp that doomed a succession of efforts to make lasting improvements to the much-maligned roadway.

Still, some see a significant opportunity.

“This really is a breakthrough,” said Sharon Bulova (D), chairman of the Fairfax County Board of Supervisors. “This is really the first time that we have been able to focus inside the Beltway, because prior to that, we’ve really run into resistance from Arlington.”

Arlington County Board Chair Mary Hughes Hynes (D) emphasized that the county has not committed to any particular outcome and that everything depends on making comprehensive improvements.

“Arlington has not changed its position on widening,” Hynes said.

Virginia is in early discussions with the federal government, which regulates the tolling of existing highways and would need to sign off on any plan. The changes would also need to be included in regional and state transportation plans. State officials say that a vote by local jurisdictions is not required but that they would not plow ahead against local wishes.

“If there’s not local support, I don’t care what the reasons are — the road’s not going to be successful,” Layne said.

Setting up the tolling apparatus would cost roughly $30 million to $50 million, according to early state estimates.

A study of the I-66 corridor and the roads around it, including Routes 50 and 29, continues, following a wide-reaching analysis completed in 2013. Researchers are trying to refine estimates on how many cars would use a tolled I-66 — and thus how much money could be raised for transit and other projects in the three included jurisdictions: Arlington, Fairfax and Falls Church. The state’s current estimate: $5 million to $25 million a year.

It’s a given for many Arlingtonians and other planning and transit advocates that the only way to truly solve congestion is to focus on drivers, bikers and walkers in a comprehensive, thoughtful way. Some advocates of road-building and other skeptics interpret that as slippery talk used by protectionists or anti-growthers to spin boutique projects or stifle progress.

Hynes said the real breakthrough now is that there is broad local and state agreement that a list of transit and other projects — she uses the wonky term “multimodal” to refer to these improvements, as in modes other than just automobiles — should be done before talking about adding more miles of concrete.

“It fits with how we approach moving people. You’ve got to give people choices. They have to be real choices, and they have to work,” Hynes said. “You can’t throw down a mile of bike trail and dump people in the busiest street around.”

Hynes points to the earlier studies of the corridor, in which “the modeling showed it moved more people more efficiently to pay attention to all the modes.” With the emerging effort with the state, Arlington has a chance to show that its approach will shine in practice, an opportunity that shouldn’t be missed, she said.

I-66 is one piece of the picture, Hynes said.

“In 2025, or right before 2025, there would be a new assessment of what’s actually going on on the road, what’s working, what’s not working,” Hynes said. At that point, she said, “There would be a conversation. The issue of, ‘Is widening a good choice or not?’ would again come into play.”

That might be consolation for commuters from Northern Virginia’s western reaches and elsewhere, who would be asked to pay the new tolls. To critics who would say it looks like the state is using commuter money to essentially buy off opponents in Arlington, “I say, ‘We have a way forward. It’s a pragmatic solution,’ ” Layne said.

I-66 “runs right through their county. As they like to put, ‘To get to Washington, you’ve got to go through Arlington,’ ” Layne said. For years, Arlington officials have been opposed to expanding interstate highways within their borders, he said, and their 2009 lawsuit helped sink efforts to stretch toll lanes on Interstate 395 through the county and toward the District line.

Negotiating is better than trying to take a hard line, Layne said.

“We could have just fought the whole way through,” he said. But “that has not generated much fruit in the past.”

Earlier this month, four Virginia congressional representatives complained about the quick movement of the tolling plan, which the Virginia Department of Transportation said could begin in 2017.

They also raised concerns about carpool changes. Currently, I-66 inside the Beltway is restricted during the morning and evening rush hours to vehicles with two or more people, with some exceptions. The tolling proposal would allow cars with one or two people during rush hours, but there would be a charge. Those with three or more would ride free.

Rep. Gerald E. Connolly (D-Va.) and three colleagues also criticized parts of a broader plan to expand I-66 outside the Beltway.

Layne emphasized that all the plans remain subject to public comment and could be changed. “We’ve been very inclusive in working with the localities from the beginning,” he said. He’s also spoken with Connolly and will brief him this week.

Last month, Arlington, Fairfax and the city of Falls Church sent a letter to the state designating the Northern Virginia Transportation Commission as the local body that would receive the toll money and distribute it to the localities for various projects.

“We don’t want the monies,” Layne said. “We want to keep them in the Northern Virginia region,” Layne said.

Bulova called the letter a “statement of intent” by the jurisdictions for an eventual tolling project. Changing the carpool minimum from two to three people “gives me a little bit of pause, because essentially what that is saying is some people won’t use I-66, or the managed lanes, because they can’t find a third passenger.”

“We’re not quite there yet. We’re still working on this,” Bulova said.

Another critical issue is whether an explicit trigger for when I-66 could be widened will be included in a deal to distribute toll revenue locally. State officials have pushed for establishing a clear metric — such as the number of cars flowing through a particular part of I-66 over a certain period — so that years from now, if traffic is bad enough there, the widening would get a green light.

But Hynes opposes including such a provision.

“I wouldn’t say, at the moment, ‘No, never’ on widening,” Hynes said. But the fixes first need a chance to prove their success or failure. “I’m not willing to pre-agree to how we measure that.”