OP-ED Why is SDOT trying to deceive the public about a potential tunnel under the Duwamish?
By Bob Ortblad
Last Wednesday SDOT presented six Duwamish crossing options to the West Seattle Bridge Citizen Task Force (CTF). SDOT’s engineering consultant WSP has been engaged to define these options and do a cost-benefit analysis on each.
Repair options 1, 2 & 3 are short-term repair options that would add 5 to 15 years to the life of the crippled bridge.
Option 4 is a rebuild of the same box girder bridge in concrete or steel on the same foundation. Option 5 is full bridge replacement as a steel truss bridge or a cable-stayed bridge on new foundations.
SDOT is attempting to deceive the public with option 6.
Option 6 is a deep-bored tunnel on the same footprint as the current high-level bridge. No one asked for this option. The citizens of West Seattle are asking for the evaluation of a shallow Immersed Tube Tunnel (ITT) located north of the Swing Bridge. SDOT has perverted this ITT solution by moving the tunnel a hundred yards to the current bridge footprint and converting it to a bored tunnel. An SDOT graphic shows a tunnel going under all four piers of the current bridge. This tunnel would need to be over 250 feet deep and over 1.5 miles long. SDOT does not tell us if this is to be a bored tunnel similar to Bertha or their vision of a deep Immersed Tube Tunnel (ITT). Any type of tunnel is completely impractical to build under the current bridge foundations, and then connect to existing elevated highway.
An Immersed Tube Tunnel (ITT) built to the north of the swing bridge:
- Is faster to build, though admittedly the connecting ramps are complex.
- Is likely cheaper to build
- is more durable with multiple sources confirming a 120 year longevity.
- Is safer in an earthquake than all the bridges they include as options
- Is safer in bad weather since it's covered.
- Could start sooner since what happens with the existing bridge is irrelevant to the tunnel.
- Can accommodate light rail easily thus offsetting the cost with Sound Transit’s help
- Won’t disturb the river in a damaging way and in fact could improve it for Salmon habitat.
I cannot believe a professional engineer would propose option 6 a deep bored as a solution. Option 6 can only be explained as a poorly executed attempt to sink a viable ITT solution.
ITT published history:
I wrote the following:
“OP-ED: The bridge is history; It’s time for an Immersed Tube Tunnel”.
On May 30
I followed up with:
“Why not a Duwamish tunnel? 20 questions answered”.
SDOT posted an RFQ for bridge engineers to design a replacement bridge.
Pressure from West Seattle citizens and Lisa Herbold forces SDOT to add a tunnel addendum to a bridge only RFQ.
KIRO Radio – Could a tunnel be the best replacement for the West Seattle Bridge?
Washington Business Alliance webinar – West Seattle Duwamish Crossing
SDOT adds the ITT option to the WSP cost-benefit analysis. At an Admiral Neighborhood Association, Heather Marx stated SDOT was adding about $250,000 to WSP contract to evaluate an ITT.
SDOT presents to the CTF six options for cost-benefit analysis by WSP. Deceptive option 6, a deep bored tunnel, is presented as possible tunnel solution.
On Wednesday CTF members grilled SDOT representatives on how option 6 was defined. SDOT answers were embarrassing and less than persuasive.
SDOT should not spend a nickel with WSP to evaluate this tunnel option. Current option 6 should be retracted and replaced with a viable ITT option north of the Swing Bridge. SDOT estimated the cost of $250,000 to evaluate an ITT at this location would be money well spent.
SDOT’s six options are silent on the possibility of a combined crossing with Sound Transit. Besides earthquake resilience, an ITT greatest advantage is the inclusion of light-rail at less cost than Sound Transit’s planned high-level crossing.
Who directed the creation of deceptive option 6?
This is hopefully an oversight, but is likely political corruption at its finest. These Goins making the decisions are getting kick backs and the higher the cost and length of time, the longer the cookie jar stays open for their greedy hands.
Anybody foolish enough to believe you deserves to be deceived. The duwamish is a federal water way. The fed only allows temporary closures for short periods with the understanding that the Marine traffic always has the right of way during normal operation.
You itt totally disregards the movement of traffic off surface streets. You can't just draw a line and say that's where it connects. The current bridge has a 6 degree rise and fall. Your itt would exceed that by double in the same length as the current bridge. Stop talking about things you know nothing about.
Sdot went to design engineers and asked for a feesable tunnel proposal.
I prefer an immersed tube tunnel.
Yes, stop talking about things you know nothing about
First the "closure" of the river as you refer to it would last roughly 12 to 18 hours as the tunnel segments are put in place. The dredging would take place just as King County does dredging only for a far shorter period of time not requiring closures. The Immersed tub tunnel does in fact take into account surface traffic. The issue of connectivity is hard to portray without 3-D software but the elevations shown are all accurate. The tunnel in fact would NOT exceed a 6 degree grade, you are mistaken and have not studied the matter enough to know. Unless you have a engineering degree, which you clearly do not, you should refrain from making assertions of this type.If you look at the proposal for the deep bore tunnel.. that was apparently not prepared by a professional engineer. It's on the order of a high school project. And by the way, it's spelled FEASIBLE.. which the bored tunnel under the Duwamish is not.