Montgomery County planners have proposed converting some lanes on the county’s busiest roads to buses-only. Eager to avoid widening roads, the planners say bus-only lanes would be a faster and more affordable way to improve transit and limit growing traffic congestion.

The idea of taking asphalt from private vehicles in one of the country’s most traffic-clogged regions is likely to draw protests from some motorists. But Larry Cole, a Montgomery transportation planner, said the county’s continued population growth will require persuading more people to forgo the convenience of driving by making buses faster and more reliable — even if that means motorists get less room on the road.

“If our future is more in transit, then that’s what should get priority in the assignment of our transportation infrastructure. . . . I think there’s been a running assumption [in transportation planning] that people want to drive, but that assumption is changing,” Cole said.

The proposal, which the County Council would have to approve, follows a national trend toward designing roads to move the most people. Traditionally, the focus has been on moving the most vehicles.

Montgomery’s plan would be among the region’s first experiments with dedicated bus lanes. Currently, there are two bus lanes — on short segments of Seventh and Ninth streets NW — in downtown Washington.

The issue is surfacing in Montgomery as county officials update long-term transportation plans to reflect a proposed network of bus lanes. Such a network has been discussed for a couple of years, but this is the first recommendation to build much of it by converting regular lanes. The planning department is scheduled to air the proposal during public meetings next week and public hearings in February.

Some critics of the proposal say Montgomery’s roads are already too jammed for motorists to lose any asphalt. Taking transit is impractical for many people, they say, and trucking and some other business-related traffic can’t rely on buses.

“Putting a mass transit system in on the cheap at the expense of the general purpose lanes is the wrong way to go,” said Lon Anderson, a spokesman for AAA Mid-Atlantic. “In Montgomery County, there’s now an enormous anti-vehicle bias. They’re more interested in getting people out of cars than moving traffic efficiently.”

Harriet Quinn, a Silver Spring resident who follows transportation issues for her neighborhood, said she’s concerned that much of the traffic that swamps the Four Corners area — heading to and from the Capital Beltway — would back up even more.

“Congestion already spills over into our neighborhood,” Quinn said. “I’d have concerns about taking lanes and how that would work.”

Cole, the transportation planner, said computer traffic models predict that travel times wouldn’t increase significantly for motorists, even with less road space, because many would ditch their cars to ride the faster buses.

The models predicted that by 2040, the evening drive from downtown Silver Spring to Randolph Road via Route 29 would take an estimated 69 minutes if buses were given no priority. If buses got their own lane, it would take a motorist 71 minutes. The morning drive on southbound Wisconsin Avenue between Cedar Lane and Friendship Heights would take motorists 15 minutes without a bus lane and 18 minutes with one, the analysis found.

Three regular traffic lanes can carry about 3,000 vehicles per hour, many of them with one person, Cole said. Because buses can carry so many more people, converting one regular lane to buses-only would allow those same three lanes to carry 7,000 people per hour, he said. Using existing lanes would avoid having to widen roads, which would require taking parts of front yards and cost about $30 million per mile, Cole said.

Planners say the biggest payoff would come on busy commuting corridors such as Rockville Pike, New Hampshire Avenue, Route 29, Georgia Avenue and New Hampshire Avenue, where the potential bus ridership from dense development would outweigh any traffic impacts.

With budgets tight and no significant new transportation funding on the horizon, planners across the country are shifting their focus from building new roads to using existing ones more efficiently, particularly by expanding bus service and improving its reliability.

A group of local officials organized by the Metropolitan Washington Council of Governments recently began to analyze where buses could run on the shoulders of local roads and highways.

The Washington Metropolitan Area Transit Authority also is studying the possibility of running buses in dedicated lanes. A 2009 analysis showed that dedicated bus lanes on particularly busy corridors throughout the Washington region would attract 100,000 new passengers, said Shyam Kannan, managing director for WMATA’s office of planning.

Michael Melaniphy, president of the American Public Transportation Association, said 55 roads in the United States have dedicated bus lanes. In some cases, buses share the lanes with carpool vehicles and taxis; in others, lanes are reserved for buses only during rush hours.

Mark Winston, a lawyer who chairs a county transit task force that recommended a network of bus lanes, said he doesn’t worry about traffic in regular lanes backing up because the panel found that one transit vehicle would take up to 72 cars off the road.

“Think about how much space that frees up,” Winston said.

Without some kind of better transit network, he said, traffic congestion will worsen and much of Montgomery’s economic development plans tied to increased transit ridership will stall.

“Is there a risk here? Yes,” Winston said. “But I think the greater risk over the long run is doing nothing.”