Helping more people to avoid driving in Maryland’s heavily congested Interstate 270 corridor would require building a network of dedicated bus lanes and eventually extending Metro’s Red Line to Germantown, Montgomery County planners say.

Their analysis — the first mass transit study for the auto-centric corridor — found that improving public transportation in the state’s most-populous county would take years and cost hundreds of millions of dollars. However, planners said their study will help Montgomery leaders prioritize transit projects as funding becomes available. That money could include a portion of revenue from the express toll lanes the state plans to build on I-270 and the Capital Beltway.

“We’re looking at how we can serve areas of the county that don’t have high-quality transit today,” said Carrie Sanders, chief of mid-county planning, during a virtual presentation Wednesday of the preliminary recommendations.

The priority over the next 20 to 25 years would be to build a network of dedicated bus lanes to feed into Bus Rapid Transit lines being designed for Rockville Pike (Route 355) and Veirs Mill Road, planners said. The dedicated bus lanes could come from repurposing traffic lanes on some roads with limited right of way — a potentially tough sell in the traffic-jammed suburbs. Planners say those decisions would be based on future engineering studies.

In the longer-term, planners said, the Red Line should be extended from Shady Grove to the Germantown Town Center, with two stations in Gaithersburg — one in Old Town and another at Route 124 near the county fairgrounds. That plan is more aspirational, planners said, because it would be expensive, and Metro officials have said they first need to expand and upgrade the rail system’s core capacity.

The I-270 corridor — the study included Bethesda, White Flint, Rockville, Gaithersburg, Montgomery Village, Germantown and Clarksburg — has grown considerably. However, planners said, it still lacks the kind of fast, reliable and frequent mass transit that would lure more motorists from their cars, better serve lower-income residents, and attract jobs and workers.

The highway, one of the most congested in the Washington region, carries commuters from job centers in Montgomery, the District and Northern Virginia to homes in Montgomery, Frederick County, western Maryland and Pennsylvania. The corridor also has dozens of biotech companies, the Universities at Shady Grove, a campus for Johns Hopkins University and the National Cancer Institute.

Marilyn Balcombe, president of the Gaithersburg-Germantown Chamber of Commerce and a candidate for county council, said she considered planners’ recommendation to extend Metro a “big win,” even if it would take years to get built.

“Unless you have the first conversation, it’s never going to happen,” Balcombe said. “We need to start the conversation.”

Residents in the mid- and upper county are hungry for more transit, she said, but living along cul-de-sacs rather than more walkable street grids leaves them with long walks to bus stops, often making transit trips slower than driving. She said she’s also concerned that taking asphalt from cars for dedicated bus lanes would worsen traffic congestion.

“That’s just not going to work,” Balcombe said.

County planners said that, even with significant transit investments, driving would remain the “primary mode of travel” for the area. However, they said, diverting more asphalt to buses that can carry 40 to 80 people each, rather than cars with one or two, is part of the county’s plan to reduce vehicle emissions that cause climate change.

“We are really prioritizing repurposing lanes over widening” them, said planner Jesse Cohn McGowan.

Running buses in dedicated lanes, planners said, would provide a faster and more reliable ride by avoiding traffic congestion — and lure more people out of cars.

The bus lanes would serve “equity focus areas” of lower-income residents, major job centers and some Metro Red Line stations. Some of the lanes would reach the areas targeted by the Corridor Cities Transitway, a Bus Rapid Transit proposal that has languished for years. However, planners said, their configuration of dedicated bus lanes would be more cost-efficient — and, therefore, more likely to be built — than the transitway plan, in part, because they wouldn’t require two costly overpasses across I-270.

Extending Metro eight miles from Shady Grove in the CSX corridor to Germantown would reduce driving the most and, in turn, best reduce environmentally damaging vehicle emissions, planners said.

“It really rose to the top in our technical analysis,” McGowan said.

But the study also revealed significant challenges, including an estimated construction cost of more than $1.4 billion. A Red Line extension also would need another 62 feet of right of way for the required safety buffer between Metro tracks and CSX freight rail tracks.

Planner Patrick Reed called the idea “exciting” but “no small feat” to carry out, even if regional and local officials championed it.

“You can think of it as the initiation of a conversation about a good idea that needs more study,” Reed said.

The Red Line would end at Germantown, planners said, to keep it along the CSX tracks, which veer west there. Continuing the Red Line north beyond the CSX corridor, they said, would have a significant environmental impact.

Other recommendations include improving pedestrian and bicycle access to transit stations and eventually moving the MARC commuter rail station from Metropolitan Grove to a new Metro Red Line station in Gaithersburg after Metro is extended. That would allow passengers to transfer more easily between the two transit systems, as well as to buses, planners said.

Another idea — extending the light-rail Purple Line west from Bethesda to Tysons — would require more detailed analysis, planners said. However, they recommended that the state keep transit in mind when rebuilding and expanding the aging American Legion Bridge as part of the toll lanes project.

“If you’re going to build this infrastructure that’s going to last about 100 years, we should have the flexibility to potentially put rail on that in the future,” McGowan said.

Maryland transportation officials have rejected that idea, saying they will improve transit by widening the bridge with express toll lanes that buses could use.

Planners also evaluated the possibility of building a monorail between Frederick and Shady Grove but said the costs “far exceeded the anticipated benefits.”

The county council would have to approve the transit plan, known as Corridor Forward. The recommendations released this month are scheduled to undergo more public discussion this fall before being submitted to the council by the end of the year.