Sound Transit to study light rail on 520?

Seattle Transit Blog reports that Sound Transit is set to spend $9.76 million in 2013 to study new light rail lines for their long range plans. While not yet confirmed, Sound Transit staff say three corridors will be studied as part of “ST3”, including a line from Ballard to UW to Kirkland with options for continuing to Redmond, Bellevue or Issaquah. Presumably, crossing Lake Washington via the new 520 Bridge would be part of the study, an idea that would have significant impacts for Montlake.

To review, the current design for the new floating bridge is “light rail ready.” That means with additional pontoons attached to its sides, trains can claim the center HOV lanes — or — an additional two lanes can be built to effectively make an 8-lane bridge. That’s the easy part.

The hard part is getting the trains between the floating bridge and UW Station. A tunnel would have to transition through water — not an easy nor inexpensive proposition. An above ground solution would have to bridge over the Montlake Cut only to arrive at UW on the surface, leaving no good options to go from there. So then, how to tunnel through and then under Union Bay?

A similar idea was once planned for the never-built R.H. Thomson Expressway, as part of its interchange with SR-520 (seen at the end of this post) in the 1960s. The plan was for a vehicle tunnel under Union Bay via a massive, man-made berm:


Images from: Roy W. Morse, Worthington Christiani Fenco, 1967.

Yes, that is an artificial peninsula with a trench leading to a submerged tunnel under the shipping channel (note Husky Stadium in the upper right). Here’s a closer view:


A man-made berm, trench and submerged tunnel under Union Bay, proposed for the ill-fated R.H. Thomson Expressway. Arboretum 520 ramps in background.

Hard to imagine these days, but apparently this was possible before there was, you know, an environment (and irony) to consider. Are we prepared to do something similar to run light rail over 520? Got a better way to get Eastside light rail to UW Station?

As Seattle Transit Blog notes, Sound Transit is moving forward with this study because Seattle keeps making noises about funding and building its own in-city light rail. ST wants to preempt the go-it-alone strategy for fear it would then loose Seattle’s tax-happy appetite for regional light rail (e.g. to Issaquah). So then, if buses using 520’s HOV lanes can get to Microsoft just as fast as light rail, is it worth the expense and possible environmental disruption to run rail through Union Bay? With Sound Transit having to balance its regional mandate, don’t be surprised if they answer “yes.”

For more on the new light rail studies, see the STB post here. See also this Slog post from 2010, and its drawing of a light rail route using the Montlake Lid and a second bascule bridge to reach UW Station. This is a non-starter, not necessarily because the City delayed the bascule bridge “for the foreseeable future,” but because it uses NE Pacific Street, which UW will never allow.