(Correction: The original version of this story incorrectly named a potential light-rail station on Northeast 12th Street as the “Bellevue Transit Center,” which is actually located on Northeast 6th Street between 108th Avenue and 110th Avenue.)

Sound Transit’s board of directors decided unanimously Thursday on a set of preferred route alternatives for the East Link light-rail system.

Debate has been going on for months over which options would work best for downtown and southwest Bellevue.

The board approved two options for the downtown area, referring to one as the “affordable alternative” and the other as the “tunnel alternative.”

The latter route would travel underground beneath 108th Avenue Northeast and stop at the Bellevue Transit Center before turning up Northeast 12th Street with another stop near the hospital district.

The “affordable alternative” would move at-grade along Main Street before heading one way in each direction along 110th Avenue Northeast and 108th Avenue Northeast with a stop at the Bellevue Transit Center. It would then hook onto Northeast 12th Street and stop again in the hospital district.

City officials are pushing for the tunnel option, saying it would cause less traffic congestion and allow the trains to move faster.

“One of the reasons we need a tunnel is for the whole regional system to work well,” said Mayor Grant Degginger. “It will make the system run more efficiently.”

The city is also concerned about how an at-grade line would impact businesses downtown.

Degginger noted that Bellevue is one of the state’s biggest generators of sales-tax revenues. He said that any adverse affects on local businesses would likely dampen Sound Transit’s ability to build out the light-rail system, since the agency is funded by that income.

Sound Transit has estimated that the tunnel option would cost an additional $500 million. The voter-approved Proposition 1 measure that funds East Link does not cover that cost.

Degginger is skeptical that taking the light-rail line underground will really cost that much.

“We (the city) believe that we’ve identified savings already for several segments that could help bring the costs down,” he said. “We don’t believe that the (cost) delta ultimately will be $500 million.”

The board voted for a south Bellevue route that would run on elevated tracks along the east side of Bellevue Way Southeast before touching down near the South Bellevue park-and-ride. It would then move at-grade to 112th Avenue Southeast and continue downtown.

Many residents opposed this option in favor of a line that would travel along the abandoned BNSF line near 118th Avenue Southeast.

Betsy Blackstock is part of a group from Surrey Downs that fought to keep light rail off of Bellevue Way Southeast. She promised to continue pushing the BNSF alternative, despite the difficulties involved with reversing course on the board’s decision.

“We will continue to work with the board and the city and continue our mission, which is to protect our neighborhood from the impacts of light rail,” Blackstock said.

The board was required to choose a set of preferred alternatives before a final environmental impact statement could be prepared. Those choices determine which options receive further analysis by engineers.

A binding decision on routing will not come until after the board has reviewed the final environmental impact statement, which is expected in 2010.