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Travel Advisory: Deck scanning on the Spokane St Viaduct may cause slowdowns

Ground penetrating radar uses electromagnetic waves to locate potential concrete delamination - or a layer of unbonded concrete - on the deck.  

We’re doing a “deck scan” of the Spokane St Viaduct to see if we need to do any work to keep it in good condition. 

**Updated 8/31/21**

The Spokane St Viaduct is the elevated street structure between the West Seattle Bridge and I-5 over Georgetown and SoDo. It’s currently open for traffic.  

A deck scan is one way we understand the condition and performance of our streets and bridges to keep them safe and durable.  

The deck scan work will affect people driving on the Spokane St Viaduct to and from the Spokane St Swing Bridge (low bridge), 1st Ave S, and 4th Ave S. This will also affect those going to and from Harbor Island via the Spokane St Viaduct. Work will take place on the Spokane St Viaduct between 4th Ave S and the SR 99 intersection. Travelers will experience slowdowns but will still be able to access these areas. 

Location of the Spokane St Viaduct. Map Credit: Google Maps. 

To perform this work safely and effectively, you can expect traffic slowdowns and lane reductions on the Spokane St Viaduct from Wednesday, September 1 to Thursday, September 2. There is a possibility that work will continue into Friday, September 3, in case crews need to finish up the segment of the bridge.

Work hours are from 8 a.m. to 5 p.m.  

We will also be doing this work on closed portions of the West Seattle Bridge and streets and ramps leading to it. 

As always, when you see people working, please drive slowly, obey signs, and use caution in work zones. 

Our contractor will be conducting the deck scan to identify any potential defects with the following tools: 

sound scan, shown below, that uses sophisticated audio equipment to listen to the road with an array of microphones. The scan notes changes in acoustic response as it drives over the roadway, which helps us identify spots on the concrete deck that may result into future potholes. 

Ground penetrating radar, shown below, uses electromagnetic waves to locate potential concrete delamination – or a layer of unbonded concrete – on the deck.  

Finally, we’ll use an overhead 4K camera to complete infrared imaging to take an in-depth view of the surface of the roadway.  

This is part of routine maintenance that we perform on all of our bridges and structures.  

Our structures all work together to keep you moving. This work on the viaduct, which is part of a larger corridor taking people across the Duwamish Waterway, helps us maintain the integrity of our transportation network. 

We are taking advantage of the decreased traffic on the Spokane St Viaduct while the West Seattle Bridge is closed to do this work so that there is as little impact on travelers as possible.