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Council hears options on Thornton Overpass project

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At Monday’s city council meeting, Robert Doherty P.E. of Shearer Design LLC of Seattle presented his firm’s findings and design options for building an overpass that would carry Thornton Street traffic over BNSF Railway tracks and connect with the Portal Way roundabout.

Dougherty presented four basic options which were different in the paths they follow and how they accommodated access to and from the Samson Ocean Systems facility, located adjacent to the proposed overpass ramp location.

For drivers, the differences between the options presented would be negligible except for the tightness of the turn as the overpass bends 90° along its path.

But cost was a notable difference between the options as indicated below. These cost figures include purchasing properties in the right-of-way, preliminary engineering and construction (in 2019 dollars):

Option Cost
1a $27,515,000
1b $26,970,000
5a $31,125,000
5b $30,525,000
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The current design options all incorporate sidewalks and a 5-foot shoulder between traffic lanes and the sidewalks along the entire length of the project.

Design issues still to be dealt with include 1) integrating a sewer line extension which is expected to run along Thornton Street from Malloy Avenue and under the railroad tracks and 2) working around poor soil conditions found in the project area.

At the earliest, construction could likely begin in 2019 assuming funding is available and there are no unexpected delays along the way. Initial estimates have construction taking about two years with much of the first year being spent mediating the poor soil conditions.

Recently, the Washington legislature included $19.2 million for this project in the 2016 supplemental transportation budget. But that has yet to be signed by Governor Inslee as he refuses to sign most bills until the legislature provides a balanced operating budget.


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