by BERNIE HAYDEN
At the Sound Transit (ST) open house in Bellevue on June 5th (materials here) ST handed a packet outlining the progress made to date toward final design. ST and the City classified the cost savings into three categories. The first and least controversial are deemed “Cost Savings Ideas Advanced for Further Engineering Review.” These generally will not affect the alignment or have any operational impact. While not “sexy” it’s useful in “keeping score” toward the $60 million City Contingency agreed to in the Memorandum of Understanding (MOU) between the City and ST.
Tunnel design and Station Optimization yielded three cost saving ideas. Utilizing a load bearing center wall can save $3m by reducing the roof structure requirements. Eliminating the Waterproofing Membrane System and allowing for routine drainage saves $2m. But I question the long term structural effects on porous concrete and structural steel. Reducing the mezzanine and platform size saves $3m. Presumably this item is moot since eliminating the mezzanine entirely seems to have the most traction and biggest savings.
Elevated guideway design elements total $16M in potential savings. Changing the Aerial Guideway Super-Structure to Precast Girder or Cast-In Place Box saves $8m. I’m not sure why this wasn’t the default and why the SR 520 segment is different. Geotechnical recommendations to optimize structural elements provides the other $8m in potential savings.
Replacing drainage structures with “low-impact development design elements” scores $2m in cost savings. I believe this comes from the Bellevue Transportation Commission and City staff design work on NE 15/16th which narrowed the street cross section from five lanes to two and made extensive use of drainage swales and pervious surfaces in lieu of the standard storm drains and retention ponds.
Perhaps not all of the ideas are totally without controversy. Expediting tunnel construction through additional road closures generates $13m in potential cost savings. Nobody is happy when their road gets closed but “living the dream” with all the current closures for 520 and the Bellevue Braids I cast my vote for more closures over a shorter period of time. Just get it over with already!
So, the score card for the category “Advanced for Further Engineering Review” adds up to $36m, not counting the $3m for reducing the mezzanine. The Executive Summary points out that engineering is still very preliminary, but even conservatively this amounts to at least $20m in savings. Still, I’m optimistic that through the Collaborative Design Process the tunnel is a done deal and there may even be money left for some “nice to have” elements.