(Sarah L. Voisin/The Washington Post)

It’s a phrase only a transportation planner could love: “person-throughput.”

The inelegant term describes the number of people who can be moved through a segment of road in an hour. It is at the heart of an ambitious proposal, to be discussed by the Montgomery County Council on Tuesday, to reserve some lanes of traffic exclusively for buses — a system known broadly as bus rapid transit (BRT).

Plans are on the books for a BRT route called the Corridor Cities Transitway, which would serve fast-growing northern Montgomery communities and businesses along Interstate 270 from Shady Grove to Clarksburg.

But planners envision a more elaborate 98-mile network of enhanced bus service on 10 of the county’s most congested roads, including Georgia Avenue from Glenmont to Olney; MD 355 (Rockville Pike/Wisconsin Avenue) from Rockville as far south as Friendship Heights; U.S. 29 (Colesville Road) from Burtonsville to downtown Silver Spring; and Veirs Mill Road from Rockville to Wheaton.

There is no money to pay for the system, which preliminary estimates indicate would cost as much as $3 billion. Nor have decisions been made on how routes would be laid out. Buses could travel in existing medians across one or two lanes, curbside or in mixed traffic.

The plan faces years of additional study, public hearings and regulatory sign-offs. It could be at least 2020 before construction begins on the first segment, which would most likely be Corridor Cities, MD 355 or U.S. 29.

But the broad outlines of this proposal — approved by the county planning board in July and tentatively scheduled for an adoption vote Nov. 26 — have emerged as the long-term transit prescription of choice. Debated in one form or another for decades, BRT is now regarded by many county leaders as the only rational way to address some of the worst commuter traffic in the country, where average peak travel times exceed 35 minutes. Road congestion is expected to grow by 70 percent between now and 2040.

Light rail is a far more expensive alternative — $75 million to $100 million a mile vs. roughly $36 million a mile for the current BRT plan — and there is little room for new roads, advocates contend.

“Nobody’s going to widen any more roads or build another Wisconsin Avenue or Georgia Avenue. You have to figure out how to take advantage of the environment you have,” said council member Marc Elrich (D-At Large), who has spent several years championing BRT.

Bus rapid transit is rooted in the notion that if you take away a lane for cars on a congested road and set it aside for attractive, light-rail-like buses, some motorists will abandon their cars. Soon, roads that were carrying one or two people per automobile will be moving groups of 200 to 500 per bus, and traffic will improve.

County planners are working out exact numbers, but they estimate that an exclusive bus lane on MD 355 from the Capital Beltway to Western Avenue, for example, could move about 600 more people an hour than car traffic in a general travel lane, based on projected ridership in 2040.

“It could transform our county,” said council member Roger Berliner (D-Potomac-Bethesda), chairman of the council’s Transportation, Infrastructure, Energy and Environment Committee. He said he wanted to see “August in Montgomery County” — meaning lighter summer traffic volumes — year-round.

Advocates preach the virtues of high-level bus service with an almost evangelical conviction. They call it a potential boon to the economically lagging eastern part of the county, which is underserved by transit and new roads. County officials pointed to a blog post this week by Metro researcher Jonathan Parker about a new analysis showing that even without a dedicated lane, Metrobus carries 50 percent of all people traveling on 16th Street NW toward downtown Washington in the morning rush — while representing just 3 percent of the vehicles on the road.

But many questions remain about the value of BRT. While it has been tried on limited scales in other U.S. cities, including Cleveland and Eugene, Ore., the long-term benefits remain more predictive than proven.

A 2012 study that the county commissioned from the Institute for Transportation and Development Policy, a New York think tank that promotes environmentally sustainable mass transit, expressed concern about the scope of the county’s aspirations.

“Montgomery County has limited experience with managing projects of this scope, scale and complexity,” the study said. “Developing even one BRT corridor will be an administrative challenge.”

While BRT is far from becoming a reality in Montgomery, residents of some neighborhoods worry that passage of the plan will give the county the legal wherewithal to take additional right of way it might eventually need for bus lanes. They’ve also expressed concern that BRT lanes will cut off left-turn access to their neighborhoods or make right turns onto main streets perilous with the combination of BRT vehicles, school buses, Montgomery Ride On buses, trucks and emergency vehicles.

“There is no way to keep frustrated drivers from cutting through our neighborhood,” especially in the morning rush hours when children are walking to school, Celesta Jurkovich told a council hearing in September. Jurkovich is president of the Chevy Chase West Neighborhood Association, which represents about 500 homes west of Wisconsin Avenue between Bradley and Drummond.

Perhaps the most contentious piece of the plan involves U.S. 29 in eastern Montgomery, which backs up for miles at rush hour with traffic — much of it from Howard County — heading toward the Beltway and the District. It reaches a notorious choke point at U.S. 29 and University Boulevard, where there are eight exits and entrances to the Beltway. It is also the heart of Four Corners, one of the region’s oldest suburban neighborhoods, and is home to Montgomery Blair High School, one of the state’s largest.

Previous road widenings have left little room to accommodate curbside BRT service without harming homes and neighborhood-serving businesses, critics say. Using the existing median would pose dangers to pedestrians on busy roads.

Harriet Quinn, who studies transportation issues for the Woodmoor Pinecrest Citizens Association, said that area is the kind of walkable neighborhood the county ostensibly seeks to emulate elsewhere.

“It puzzles me,” she said. “I’ve concluded that this has more to do with facilitating development than facilitating transportation,” she said, referring to the new White Oak Science Gateway project, a joint venture of the county and Percontee, a private developer, to create a center for medical and life sciences research east of U.S. 29 on Industrial Parkway.

Nevertheless, the plan that passed the council’s transportation committee included the study of “dedicated lanes” for the Four Corners area, sparking vigorous debate at a hearing this week.

Council member Nancy Floreen (D-At Large) said BRT is only practical in Four Corners “if you want to wipe out the community, sure. You want to take out the shopping center and the church there, sure.”

Berliner said the county needed to at least explore the idea.

“If rapid transit is going to be a reality for the 29 corridor,” he said, “we need to work our way through this issue.”