The debate isn't about the Seattle waterfront--it's about downtown Bellevue, where city leaders want their forthcoming light rail to pass below downtown, while Microsoft wants it to stay above ground in hopes of saving money and reaching its Redmond campuses. Tunneling provides the obvious advantage of not having a set of elevated tracks running through the middle of downtown (though who doesn't love the charm of Seattle's monorail?), or of having to deal with train/car conflicts on the surface.
The real shocker of the debate, though? Sound Transit project manager Don Billen "recently said motorists would have traffic-signal priority over trains." WTF, mate?! Did voters approve light rail so it could stagger through downtown surface streets like an electric bus? (Even the SLUT has signal priority, though it may not for long.) The whole point is to move a lot of people fast by taking them out of traffic.Finally, transit fans who want to do some more hand-wringing should check out this map (found via Seattle Transit Blog) of what Forward Thrust would have provided (it includes rail to Ballard and West Seattle). Forward Thrust was the largely-federally-funded transit package that twice failed at the King County ballot box--one time because of the ridiculous requirement for a 60% passage rate (it got just over 50%). Atlanta got the money instead and built MARTA.