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Photo of the S 277th Street Bridge.
S 277th Street Bridge No. 3126.

Photo of the S 277th Street Bridge, view from S 277th Street.
S 277th Street Bridge, view from S 277th Street.

Project overview

This project replaces the 70-year-old S 277th Street Bridge No. 3126 over Mullen Slough with a four-sided concrete box culvert. The 16-foot-long bridge is located on a four-lane principal arterial road that connects Interstate 5 to State Route 167 in Kent and Federal Way.

Why King County is replacing this bridge

This existing S 277th Street Bridge is load-restricted and unable to support certain types of large trucks including some types of fire engines used by adjacent fire districts, full-size garbage trucks, dump trucks, and concrete mixers. The replacement culvert will provide unrestricted access for all vehicles. It will also provide environmental enhancements by improving fish passage and removing creosote timber pilings from Mullen Slough.

S 277th Street at this location has a traffic volume of about 23,000 vehicles per day, of which 2,600 vehicles are trucks carrying an estimated 4 to 10 million tons of freight per year. This road is a designated county snow/ice route, lifeline route, and Green River Valley flood evacuation route.

Project schedule

Construction will begin in spring 2021 and is expected to last approximately three months. Due to high average daily traffic on S 277th, and unfavorable detour routes, the existing bridge will remain open with travel lane reductions through the construction zone.

Project budget

The estimated total project budget is $2.9 million. This project is funded through the King County Capital Improvement Program.

Project documents

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Contact us

Broch Bender, Communications Manager
Desk 206-263-1189


S 277th Street Bridge project location map.
Map of the S 277th Street Bridge Replacement Project location. Larger view JPG 1MB

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Frequently asked questions

Weight Limit for Single Unit Vehicles:

4 Axles - 24 T
5 Axles - 27 T
6 Axles - 31 T
7 Axles - 34 T
A replacement culvert was selected instead of a replacement bridge span because the box culvert provides a cost-effective, environmentally-friendly crossing that is much easier and quicker to install than a column (over 100-feet deep) supported bridge.
This project will be a bid-out contract project and currently is budgeted to be built in summer 2021. The total project budget is $2.9 million. The project is funded by King County.
S 277th Street will be reduced from four lanes to two lanes at the bridge. The existing bridge is wide enough to reduce the traffic pattern to one lane of traffic in each direction and shift all traffic to one half of the bridge while the other half of the bridge is demolished and replaced.

  • Stage 1
    Either the north half or south half of the existing bridge will be demolished and replaced during Stage 1 construction while the traffic is shifted to the other half of the bridge.

  • Stage 2
    Stage 2 of construction would move traffic to the newly constructed half of the new structure, demolish the remaining half of the existing bridge, and finish constructing the remaining half of the new structure.

  • S. 277th Street both directions (eastbound and westbound)
    King County will place warning/advisory signs informing drivers of reduced lanes and reduced speed limit ahead.

  • Nearby roadways
    King County will place signs notifying drivers of upcoming and current project construction and construction impacts.

  • Check King County's My Commute Map
    All lane reductions will be listed in advance on the King County My Commute map.