Opponents of Maryland Gov. Larry Hogan’s plan to relieve traffic by building toll lanes on the Capital Beltway and Interstate 270 are pushing for more legislative scrutiny on what the governor has said would be the largest public-private partnership in the country.

The opponents — mostly environmental groups, residents and public officials from Montgomery and Prince George’s counties — say the state should also have to complete an analysis of the lanes’ potential environmental and community impacts before soliciting teams of companies to build them.

If passed, a legislative proposal that has been approved by the Maryland House and is pending before the Senate would delay — but not stop — Hogan’s plan. Supporters of the bill say it would provide more accountability and transparency on projects that would affect the state for decades; the Republican administration says it would unnecessarily add hundreds of millions in costs.

Maryland Transportation Secretary Pete K. Rahn said during a Senate hearing on the bill Wednesday that holding off on soliciting private companies until after the environmental study is finished would delay the toll lane project by at least two years. That would cost motorists $2.6 billion — $1.3 billion annually — in wasted fuel, lost time and other costs of congestion, he said, and probably would add $300 million in construction costs annually to a project expected to cost a private partner $9 billion to $11 billion. Any increase in interest rates also could add hundreds of millions of dollars to construction, he said.

Rahn told the Senate Budget and Taxation Committee that by 2040, Washington-area motorists will face daily traffic congestion worse than the massive backups that ensued last week after a fuel tanker overturned on the Virginia side of the American Legion Bridge.

“If we want to experience one of those events every day, then the solution is to do nothing,” Rahn said as about 50 toll lane opponents looked on. “Hundreds of thousands of commuters would testify that something needs to be done in the region.”

But opponents say the Hogan administration is moving too quickly and ignoring local concerns about a project that many residents don’t want and fear could destroy homes and businesses if the highways have to be widened to accommodate up to four new lanes each. Many criticized the state for rejecting transit options that they say would get more people out of their cars. They say Maryland law regulating public-private partnerships should allow for more General Assembly oversight of such proposals and permit the public to view their potential impacts before the state begins to forge partnerships with profit-driven companies.

The bill “restores practical common-sense oversight to a project that many here feel is getting out of control,” the bill’s sponsor, Del. Jared Solomon (D-Montgomery), said at a gathering of opponents before the Senate hearing.

Prince George’s County Council member Dannielle M. Glaros (D-District 3) noted that the toll lanes project would be the first in Maryland to begin as a public-private partnership. The Purple Line light-rail line is also being built via such an arrangement, but it came about after the project had been studied and debated.

“We need to be fiscally responsible,” Glaros said. “We need to make sure we protect our communities. . . . This matters to every one of those homeowners just on the other side of those [sound] barrier walls.”

If the bill passes before the legislative session ends Monday, it is expected to provoke Hogan’s veto. Lawmakers could choose to override his veto when they reconvene in January.

Rahn told the committee the study so far shows a “small number of homes being impacted,” but the state won’t know the actual number until it selects one of the private teams’ designs in 2020. He said firms will be awarded extra points in the selection process for sparing homes and that he expects “even that small number of homes will be greatly reduced” in their designs.

He said the state doesn’t have the money to expand transit because doing so would require ongoing subsidies.

Maryland, Virginia and other states have begun to increasingly use public-private partnerships as a way to build major infrastructure and expand road and transit networks on tight government budgets. Teams of private companies design, build, operate and maintain the projects, and often help finance their construction, in exchange for keeping the toll revenue or, in the case of transit projects, ongoing government payments.

In announcing the toll-lane plan in 2017, Hogan said a public-private partnership would provide the Washington suburbs with badly needed traffic relief at no cost to the state.

The Maryland Department of Transportation is scheduled to hold public workshops this month on the final seven alternatives under consideration as part of the federally required study of their environmental and community impacts. The state plans to begin soliciting companies’ proposals for how and where the lanes would be built while that study is completed.

Rahn said that this spring, the state plans to ask the Maryland Board of Public Works — which is composed of the governor, comptroller and state treasurer — to approve the project as a public-private partnership. That would allow the state to solicit proposals and choose a winner in 2020, and sign a contract by late 2020, he said.

Under current law, Maryland agencies that want to build a transportation project via a public-private partnership must submit a “pre-solicitation report” to the state’s legislative budget committees and the General Assembly’s Department of Legislative Services for review before asking the Board of Public Works to approve it. The law does not address when any environmental review must be completed.

Gary Hodge, a former Charles County commissioner and transit activist, said passage of the bill would show “legislative sentiment,” making it harder for Hogan to seek Board of Public Works approval to begin the solicitation process.