Just as Bellevue and Sound Transit are approaching agreement on ways to cut costs on the planned light-rail line from Interstate 90 through downtown Bellevue, two citizens groups, Building a Better Bellevue and Friends of Enatai, have gone to court to try to block that route.

Just as Bellevue and Sound Transit are approaching agreement on ways to cut costs on the planned light-rail line between Interstate 90 and downtown Bellevue, two citizens groups have gone to court to try to block that route.

Building a Better Bellevue and Friends of Enatai claim in a lawsuit filed Tuesday in U.S. District Court that the federal government’s approval of the route violates federal environmental law and a law intended to protect parks and historic sites.

Defendants are the Federal Transit Administration, the Federal Highway Administration and Sound Transit.

The suit was filed one day after the Bellevue City Council learned that staff and elected officials from the city and Sound Transit have reached a tentative agreement on which cost-saving concepts should be studied in detail.

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City Council members involved in the cost-saving exercise said representatives of the two jurisdictions are recommending these plan changes for further study:

• Relocating the downtown station from an underground site beneath 110th Avenue Northeast to a surface location beside Northeast Sixth Street, where the rail line emerges from a tunnel. A less-expensive underground station, with one rail line above the other, will also be studied.

• Protecting the historic Winters House on Bellevue Way Southeast by moving the rail line from a trench to the surface and shifting the tracks and roadway to the west while the city builds a southbound HOV lane.

• Making the rail line less intrusive to the Surrey Downs neighborhood by raising 112th Avenue and running tracks below it rather than building a longer, elevated rail structure.

Officials are discussing whether the rail line should dip into a trench so the tracks wouldn’t block the neighborhood’s connection to 112th Avenue.

Those changes, combined with less-visible design revisions, could cut the cost of the $2.8 billion East Link rail project by $41 million to $68 million, according to initial estimates.

As much as $60 million in savings would be subtracted from Bellevue’s $160 million commitment toward a short downtown tunnel.

The Sound Transit Capital Committee will review the ideas Thursday and the Bellevue City Council will make recommendations next Monday.

The Sound Transit Board is scheduled to decide on June 28 which concepts to study in detail as alternatives to the adopted plan.

City Councilmember Jennifer Robertson, who is working on the design with a small group of council members and Sound Transit board members, said Wednesday the two sides have “a very strong” working relationship, and, “everyone is really working hard towards a common goal.”

Final route decisions will be made next year. When completed in 2023, the East Link line will connect Redmond, Bellevue, Mercer Island and Seattle.

The lawsuit by Building a Better Bellevue (BBB) and Friends of Enatai said Sound Transit’s plan jeopardizes the Mercer Slough wetlands and the historic Winters House, violating a 1966 federal law that protects parks and historic sites “unless there are no feasible and prudent alternatives.”

Sound Transit failed to adequately consider alternatives including a deep-bore tunnel, a route east of Mercer Slough, or a nonrail project, the citizens groups said.

Sound Transit spokesman Geoff Patrick said the agency believes its environmental analysis of East Link “met if not exceeded the requirements of the law,” and said he doesn’t expect the lawsuit to delay the start of construction, scheduled for 2015.

The plaintiffs oppose construction of a rail line along Bellevue Way and 112th Avenue, and BBB last week proposed a deep-bore tunnel it said would be less expensive than the official plan for a trench and an elevated segment.

But Sound Transit said the nearly two-mile tunnel proposed by BBB would be more expensive than the current plan.

While BBB claimed the tunnel would reduce contingency and professional services costs by $101 million, the transit agency said tunneling is a higher-risk form of construction that generally calls for a larger contingency fund.

BBB members said Wednesday their calculations were conservative and based on Sound Transit methods for computing costs.

Keith Ervin: 206-464-2105 or kervin@seattletimes.com