The boldest new concept would abandon the 2011 proposal to excavate a huge underground station downtown, perhaps 70 feet deep with a mezzanine, beneath the intersection of Northeast Fourth Street and 110th Avenue Northeast. Instead, Sound Transit would look at a shallower Bellevue Transit Center Station for the East Link route.
Builders could exploit the slope that descends from the financial district to Interstate 405 — where tracks are supposed to emerge from the tunnel anyway, then become elevated near Meydenbauer Center. One layout involves a so-called “diagonal” station that cuts the corner where there’s now a City Hall parking garage and vacant King County land. The second concept is oriented east-west along Northeast Sixth Street.
Engineers are also looking at ways to save money at the 110th Avenue Northeast location by making the station shallower or narrower.
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Either of the shallow stations would be about one block east of the existing bus hub, and train platforms would be closer to street level.
In other words, a layout more like Seattle’s International District/Chinatown Station and less like the University Street Station.
Besides saving money, a shallow station might improve transit operations by making the trackway more level as it emerges toward I-405 and the hospital district. A deep station would have required a 6 percent climb for trains continuing east, said Don Billen, deputy project director, in a news briefing Wednesday. Officials don’t know yet if there are any negative effects from a shallow station, said Ron Lewis, East Link executive project director.
Officials don’t know what the savings might be, but said the “first $60 million” of savings would reduce what Bellevue must spend to help fund the tunnel — implying they are thinking in eight figures.
A major challenge will be digging the tunnel using a cut-and-cover method that tears up 110th Avenue Northeast, while keeping east-west traffic flow, and allowing businesses to maintain car access, said Bernard van de Kamp, a Bellevue assistant transportation director. Heavy construction is to start in 2015 and last several years.
The concepts will soon be converted to visuals and shown to the Bellevue City Council, transit board, and in public forums this spring, with a decision due by July, said Lewis. The springtime research will be done by a team of engineering firms and overseen through an elaborate structure of government committees.
Tunneling has been forecast to cost up to $320 million more than elevated or surface tracks, but the city agreed to cover half the increase. Voters approved a $2.7 billion [2007 dollars] project without tunnel funds, from Seattle via the I-90 floating bridge to Overlake Transit Center, in 2008. Trains won’t be running until 2023.