The deal between Maryland and Virginia to build a new, wider American Legion Bridge represents a victory for both regional cooperation and the battle against gridlock, but let’s pause and think before popping the champagne.

Although a fix is surely needed at the region’s worst traffic bottleneck, the plan unveiled last week raises two important concerns.

First, is it smart to keep investing in roads and cars in an era of accelerating troubles owing to climate change? Environmentalists and other critics say the two states would do better to spend their time and money on expanding transit options.

Second, is the public getting a good deal in the long run by relying on tolls collected by private companies to finance bridges, highways and similar projects? Some transportation experts see risks that the tolls will be painfully high and self-defeating, or that the project won’t be financially viable a decade or two from now.

Despite these worries, there’s no doubt the accord marks a breakthrough. The 56-year-old bridge on the Capital Beltway connects Montgomery and Fairfax counties, the region’s two most populous jurisdictions. Calls to rebuild it have grown acute in recent years, as lengthy backups became routine.

No one was predicting progress until Tuesday’s announcement, which Maryland Gov. Larry Hogan (R) and Virginia Gov. Ralph Northam (D) sprang as a surprise after several months of secret talks. Hogan had seemed less interested in the bridge than in his plan to add toll lanes to widen Interstate 270 and Maryland’s half of the Beltway. Virginia leaders had consistently said it was up to Maryland to fix the bridge, because the Free State owns nearly four-fifths of the span, as well as the Potomac River beneath it.

The impasse was a prominent example of the insular thinking — each jurisdiction focused only on itself — that too often has led to dysfunction in the Washington region. But the two governors crafted a compromise.

Virginia agreed to take on the burden of financing significantly more than 21 percent of the project, even though its ownership stake in the bridge is 21 percent. That was politically feasible partly because Virginia, like Maryland, plans to avoid putting any taxpayer money into the project. Instead, both will contract with private companies to build and operate the bridge through public-private partnerships, or P3s, with the entire cost covered by future toll revenue.

Maryland agreed to speed up the schedule for hiring a contractor to widen not only the bridge but also its portion of the Beltway stretching from the bridge to the Interstate 95 interchange in College Park. That appears to lessen the prospect that cars using the expanded bridge will just get stuck in the same Beltway gridlock on the Maryland side.

The new bridge will have four express toll lanes in addition to eight free lanes, as the current bridge has. Officials said it will cut commuting time in half for many travelers and reduce congestion in the free lanes by 25 percent. Construction is expected to begin in 2022.

Area leaders hailed the accord as the latest in a string of successes that reflect a new commitment to regional cooperation. Last year, Virginia, Maryland and the District joined to approve $500 million a year in dedicated funding for Metro. Then Amazon said the three jurisdictions’ willingness to cooperate helped persuade it to select Arlington as the site of its second headquarters. In September, the Metropolitan Washington Council of Governments (COG) agreed on a regionwide plan to increase production of affordable housing for low- and middle-income residents.

“It turns out regional cooperation is the new normal,” COG Executive Director Chuck Bean said. “We’ve been waiting 20 years for this kind of thing.”

Jack McDougle, president of the Greater Washington Board of Trade, called the American Legion Bridge deal “huge” and added, “There’s been a number of issues across the region that have been problematic for a long time, and I think now we’re starting to align with a much more collaborative effort in addressing those issues.”

Still, skeptics raised environmental and financial questions about the project.

In a letter to Hogan and Northam on Friday, leaders of three environmental groups expressed “grave concerns” about widening the bridge, I-270 and the Beltway.

“In the era of the climate crisis, making room for more greenhouse gas emitting vehicles on our roadways is irresponsible 20th century planning to address a 21st century problem,” wrote the leaders of the Audubon Naturalist Society, Potomac Conservancy and Rock Creek Conservancy. “We need to implement solutions that move people around our region with net zero climate impacts.”

Stewart Schwartz, executive director of the Coalition for Smarter Growth, said that congestion at the bridge definitely needs to be addressed, but that his group would like to see a comprehensive strategy including more reliance on bus, rail and carpooling as well as more housing built near transit.

“They’re focusing on the right area. The question is how they’re going to solve it,” Schwartz said. “From what we can tell, it’s mostly moving bottlenecks.”

The new bridge includes a transit option because public buses will travel free in the toll lanes. Negotiations with the private concessionaires will determine whether high-occupancy vehicles will have to pay.

The bridge will have pedestrian and bicycle access. Maryland Transportation Secretary Pete K. Rahn said 10 percent of the toll revenue will be shared with local governments, which can use it to finance transit if they like.

Jason Miller, chief executive of the Greater Washington Partnership, said it was a “false choice” to say the region should invest in either roads or transit, because both are needed.

“Our approach has been that we need multiple options for people to move around the region,” Miller said. Those include Metro, commuter rail and buses, but also cars.

Miller added: “We can’t just say we’re going to tackle this by focusing on one piece of the puzzle.”

The financial concerns center on the effectiveness and risks of P3s. They fulfill a politician’s dream by offering the chance to get credit for building a big project at little or no cost to the taxpayer. That’s because the financing is borne by private partners, who are repaid with toll revenue in the long run.

Virginia already is using P3s for its high-occupancy toll lanes on the Beltway and I-95. Maryland is using one for the light-rail Purple Line.

But some experts warn that the highly complex deals can sour for the public if they are not structured properly. If the state puts up none of the money upfront — as foreseen in the American Legion Bridge project — then the private contractor may have to charge such high tolls that the express lanes will be little used.

“Complaints about future tolls in the $30 to $40 range are legit,” said John Forrer, director of the Institute for Corporate Responsibility at George Washington University. “Depending on the cost of the construction, the fees and the traffic have to add up enough to cover the debt burden, and could be a high number.”

Also, if the project proves unprofitable in the future, the state might be asked to provide a bailout or see the company go bankrupt.

“The concern is, are they structuring the deal in a financially sound way?” Forrer said.

Rahn said such concerns are unfounded.

“The idea that the lanes will be little used is simple-minded,” he said. “The concessionaire is a business that must have a reasonable priced service in order to recoup their investment.”

If the concessionaire fails, he said, then bondholders would assume operation of the toll lanes.

“The state has no liability under any circumstances,” Rahn said.

The public will want to look closely at the state’s contracts with the private companies to ensure that’s correct.

And the region will want to aggressively expand transit alternatives to gradually reduce its dependence on climate-killing cars.