The Bellevue Council will take a closer look tonight at a new south Bellevue alignment for East Link light rail that would slice across the middle of Mercer Slough Nature Park. The new route would allow the train to pick up passengers both at the South Bellevue Park & Ride and the Wilburton Park & Ride, while avoiding neighborhoods along Bellevue Way.

The "B7 Modified" design concept hasn't been mapped yet. Bernard van de Kamp, regional projects manager for the city, said the proposed route would go from Interstate 90 to the South Bellevue Park & Ride, go directly east across the slough, then turn north near where a King County Metro van pool maintenance yard is located. From there, the train would follow a Burlington Northern railroad right-of-way along Interstate 405 for a stretch, then bear slightly west to meet up with the Wilburton Park & Ride.

Van de Kamp said the route across Mercer Slough would probably be elevated, but just how difficult it would be to build an elevated train route through the middle of a wetland is not known. "There are definitely some complications," he said.

The slough's peat-like soils are likely to be an engineering problem no matter where light rail goes; the slough's western boundary is along Bellevue Way Southeast, one of the proposed alignments, and its southern boundary is along I-90 between Bellevue Way and I-405, another one of the proposed alignments.

Sinking soils in Mercer Slough have long been a problem for the city. In 2002, Bellevue spent $3.8 million to stabilize Southeast Eighth Street, which had sunk in the soft muck.

The council could vote tonight to send a letter to Sound Transit endorsing the south Bellevue route, as well as a route through downtown Bellevue. The meeting begins at 6 p.m.