Building a 16-mile Purple Line through Montgomery and Prince George’s counties would require condemning 31 homes, 43 businesses, and parts of hundreds of yards and other parcels of land, said a new state report that includes vastly higher community impacts than previously made public.

In total, building a light-rail line, Metro stations and two train storage and maintenance facilities would require the state to buy and condemn all or part of 342 properties along the east-west route between New Carrollton and Bethesda, the Maryland Transit Administration said.

In an analysis released in 2008, state officials estimated that the line would require condemning a dozen houses and apartment buildings and 16 to 19 businesses. Although that analysis noted the need for “strip acquisition” of other adjacent parcels, it did not give a total number of properties affected.

MTA officials said they discovered more affected properties, particularly in the Riverdale area, after they did more detailed engineering.

“To the extent we can minimize [the affected properties] as we go along further in the project, we will,” said Henry Kay, who oversees transit projects for the MTA.

But which homes, businesses and yards are being eyed for condemnation remains mostly unknown. MTA officials declined to release the information, saying it includes property value estimates that could become part of future negotiations. According to the state, construction won’t begin until 2015 at the earliest.

Kay said the list will remain in flux during the next year of preliminary engineering, while the route — and the properties it would affect — continues to be refined.

Publicizing a list before then “gets people concerned needlessly because it can change the next day,” Kay said. “There’s nothing to hide here, but until it’s really a fixed list, we’re not going to go out and notify every one of those people.”

Kay said the MTA has notified property owners whose land or buildings can’t be avoided. But homeowner groups and local officials along the route said they need more information.

“It creates a lot of hysteria for people, who naturally are very concerned,” said Montgomery County Council member Valerie Ervin (D-Silver Spring), whose district is in part of the proposed route. “We don’t have any information to say these homes on this street are going to be taken. They should tell people as soon as possible so people can make decisions.”

Phil MacWilliams, president of the Coquelin Run Citizens Association in Chevy Chase, said the MTA should release the addresses while there’s still time to make significant changes to the line.

“In our community, there are at least 40 homes along the [Purple Line] right of way,” MacWilliams said. “Everyone is very concerned whether they’re in the cross hairs of the Purple Line.”

State transit planners included higher community impact numbers to the Federal Transit Administration in August as part of their ongoing application for federal funding. Kay said the report, which listed 322 affected properties (the number has since risen), was posted on the state’s Web site in October, after the FTA granted permission to proceed with more engineering. The state is seeking federal money for half of the line’s construction costs, estimated at $1.93 billion.

State transit planners have long said that trying to thread the two-track light-rail line through Washington’s inner suburbs would be challenging. The line was intentionally routed through densely populated areas to serve the most riders, but that also brings trains close to homes, yards and shopping centers. Running light-rail trains on local roads often requires widening the streets. State transit planners have said building extensive tunnels is too expensive.

Adding to the difficulty is that most of the Purple Line hasn’t been part of local development plans for long, leaving little preserved right of way beyond the Georgetown Branch trail between Bethesda and Silver Spring — a segment that has sparked its own controversy.

Harry W. Lerch, a Bethesda land-use lawyer who specializes in condemnation litigation, said Maryland law doesn’t require the state to give a certain amount of notice when buying and condemning property under its powers of eminent domain. The law only specifies when and how the state is allowed to take possession of the property, he said.

Lerch said he had a client who didn’t realize that his home was in the path of the newly built Intercounty Connector until a state official knocked on his door with an appraisal and a contract to sign. Transportation planners typically wait until most of the engineering is done before notifying property owners, he said.

Lerch said his firm worked over several weeks to compile its own list of 230 property owners affected by the planned Purple Line route.

He said his firm plans to notify those owners in hopes of generating business but declined to release the list because it is not official.

Lerch said he found the most impacts in Riverdale, where the state proposes to widen East-West Highway (Route 410) east of Kenilworth Avenue (Route 201) and along Kenilworth.

“That’s a tricky area,” Lerch said, “because it’s totally built out.”

Joe Brice, president of the Prince George’s County Civic Federation, said many residents would welcome better transit but are concerned about a light-rail line destroying homes and forever changing neighborhoods.

Once state officials release a list of properties being considered for condemnation, Brice said, “the protest against [the project] will increase. . . . I’m quite sure they understand that.”

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