Monday, January 11, 2021

Southbound SR 99 Duwamish River Bridge work in Seattle to start in February

By Tom Pearce

We have a contractor for work on Seattle's southbound State Route 99 Duwamish River Bridge, aka the First Avenue South bridge, but we don't have a date when work will begin. The current estimate is early  February; once we have a specific date we'll share it on our website and Twitter.

Massana Construction Inc. of Gig Harbor had the lowest bid among the five contractors who submitted proposals. Their bid of roughly $380,000 was actually about 18 percent below our engineer's estimate. The savings will be available for us to use on other projects.

With the West Seattle Bridge closed, we understand how important the SR 99 Duwamish River Bridge is to people who travel to or from West Seattle. We are working closely with the Seattle Department of Transportation as we plan for and schedule repairs.

Repairs coming
When this work begins it will only affect southbound SR 99; the northbound lanes will remain open at all times. While we're working, several alternative routes are available.
The bearing pads that the bridge girder rests on are worn out and need to be replaced
on Seattle's SR 99 Duwamish River bridge.

Our contract allows the bridge to be reduced to two lanes for 15 consecutive 24-hour days. At the start of the project we will need to close all lanes of southbound SR 99 between 10 p.m. and 5 a.m. for one night so our contractor can set up their equipment. Travelers can expect about three weeks with the southbound bridge reduced to two lanes. We'll also need a full overnight southbound closure at the end of the project to remove equipment.
When we reduce the southbound SR 99 Duwamish River Bridge to two lanes, people have
several options to get around the closure.

During the work, Massana's crews will replace bearing pads, which allow the structure to flex and move with weather and traffic conditions. They'll also do some steel repair and concrete bridge deck repairs. To accommodate this, crews will shift traffic to one side of the bridge first, then move traffic to the other side to finish.

Why we're working now
The bearing pads – masonry pads that the girder rests on – were part of the initial construction when the southbound SR 99 Duwamish River Bridge opened in 1996. These pads are worn out and need to be replaced. The pads allow us to precisely set the elevation of the bridge's superstructure.

When a truck is on top of the bearing, it presses the deck down. When the truck moves, you can see the deck rise slightly.

During a regular inspection in October 2020, our bridge maintenance crews noted the bridge was moving on the bearing pads more than it should, so we did temporary repairs to keep the bridge stable while we planned the permanent fix.

There's never a good time to reduce capacity on a major highway. However, scheduling this work allows people to plan ahead and consider alternate routes. It also helps us avoid the need for emergency repairs that require unscheduled closures. Thanks for your patience as we complete this vital work!