Planning leaders from Montgomery and Prince George’s counties refused Wednesday to sign off on a study of how to add toll lanes to the Capital Beltway and Interstate 270, saying the state has not addressed their concerns about the plan’s finances, potential environmental impacts and lack of significant transit options.

The unanimous rejection by the Maryland-National Capital Park and Planning Commission demonstrated broad local political opposition to the traffic relief plan by Maryland Gov. Larry Hogan (R) and hinted at potential lawsuits against the project. That could include a legal challenge from Montgomery planning officials, who said they would fight any attempt to use the state’s power of eminent domain to condemn public parkland to widen the Beltway.

Moreover, local political opposition and even the suggestion of a protracted legal battle could spook the private companies and financiers whom the Maryland Department of Transportation plans to pursue to build, finance and operate the toll lanes as part of a public-private partnership. It took just one lawsuit to delay construction of Maryland’s light-rail Purple Line, also being built through a public-private partnership, by a year and potentially add hundreds of millions to its cost.

The planning board members, who are appointed by both county councils, told Maryland highway officials that they could not “concur” with the state continuing to study highway expansion options that would violate their transit-oriented growth plans and destroy environmentally sensitive parkland.

Commissioners said they are also frustrated that they haven’t learned much since their initial “nonconcurrence” vote in June, including the toll rates the state has assumed to justify the lanes’ financial success.

“I’m not getting the impression you’re really hearing our concerns,” said Elizabeth M. Hewlett, chair of the Prince George’s County Planning Board.

Hewlett said she had found the state’s responses so far, including an assertion that local officials didn’t understand the environmental review process, to be “tremendously offensive” and “very demeaning.”

“We need some information,” Hewlett said.

After the meeting, Lisa Choplin, the state’s project director, said it would be “ideal” if the state could show the Federal Highway Administration a “partnership” with local officials. Even so, she said, Wednesday’s rejection would not stymie the toll lane plan.

“We’ll certainly come back at some point to seek their concurrence,” Choplin said, “but it’s not something we need to move forward.”

The Hogan administration has proposed adding up to two toll lanes in each direction to I-270 and the Beltway, including replacing and expanding the American Legion Bridge between Maryland and Virginia. Toll prices would adjust to keep traffic in the toll lanes flowing freely at a minimum of 45 mph, officials said. The regular lanes, which would be rebuilt, would remain free.

Under the state plan, teams of companies would build the toll lanes, finance their construction and operate them in exchange for keeping most of the toll revenue and at no cost to the state. With the lanes estimated to cost $9 billion to $11 billion, it would be the largest public-private partnership in the United States.

During Wednesday’s joint meeting in downtown Silver Spring, the Montgomery and Prince George’s planning boards voted unanimously not to endorse the state’s decision to further narrow the alternatives it will continue to analyze.

How much local cooperation the state needs is one issue that, if not resolved, could end up in legal challenges. The other is whether the state has the legal authority to condemn and seize public parkland under its power of eminent domain.

After the meeting, Montgomery County Planning Board Chairman Casey Anderson said the commission must protect its parkland and seek more transit options in keeping with local growth plans aimed at limiting sprawl development.

Asked whether the state needed the counties’ approval to pursue the project, Anderson said: “That’s among the many issues we may have to fight about in court. It’s crystal clear that we own a lot of land that they need, and our willingness to part with it is a big issue to be addressed.”

As for the question of how far the state’s powers of eminent domain reach, Anderson said, “I feel very confident we have a strong legal position that they are utterly without authority to take our land.”

Hogan spokesman Michael Ricci responded to the “no” vote by saying that state officials have consulted with local leaders on the tolling plan. “Maryland and Virginia are working together in a bipartisan way to fix the entire Capital Beltway, and the response has been overwhelmingly positive,” Ricci said in an email. “State officials have met with Montgomery County officials on numerous occasions, and we carefully studied their alternative. Instead of being constructive, they are recklessly scheming to keep the region stuck in some of the worst traffic in the country.”

Maryland highway officials recently dropped a more limited expansion option that would have added one toll lane to the Beltway in each direction, rather than two, and converted I-270’s HOV lane to a toll lane. Doing so would not relieve traffic congestion as much as other options and would require a $600 million state subsidy due to lower toll revenue, state highway officials said.

They said they also have rejected a Montgomery proposal to avoid private homes and parkland along the Beltway east of I-270 by funneling that traffic onto the Intercounty Connector (ICC) toll road to the north.

Jeff Folden, the project’s deputy director, said the ICC would not have enough capacity after 2030 to absorb that traffic. He said many motorists also would have to drive too far out of the way, while the most congested part of the Beltway would not get relief.

Neither option is the kind of “reasonable” alternative the state is required to study further, Choplin said.

The draft environmental impact study of the toll lanes on I-270 between the Beltway and I-370 and on the Beltway between the Virginia side of the American Legion Bridge and Route 5 will be released this spring, Choplin said. Construction will begin in late 2022 at the earliest, she said.

Choplin said the state is preparing to start the environmental study for I-270 between I-370 and I-70 in Frederick.