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S 277th Bridge No. 3126 Replacement Project

Project completed

277th Street Bridge.

King County completed major construction on the 277th Street Bridge Replacement Project on Friday, November 19, 2021. All lanes of traffic are now open.

Status update

Monday, November 22, 2021

Major construction on this project is now complete, and all lanes of S 277th Street are open. The few remaining items of work include restoring plants and bushes alongside the road. The planting work may require daytime single lane restrictions through the end of the month.

En Español

Esta pagina web - 28 de mayo de 2020 Download PDF document (1MB)

Determinación de no Impacto Adverso Significativo al Medio Ambiente (DNS por sus siglas en Inglés) - Fecha de emisión, 28 de mayo de 2020 Download PDF document (198KB)

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.

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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.

Photo of the S 277th Street Bridge.
S 277th Street Bridge No. 3126 prior to construction.

Construction timeline

  • Utility relocation: June 2021
  • Equipment on site: July 2021
  • Construction begins: July 2021
  • Construction complete: November 2021

Getting through the construction zone

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

Project flyer

S 277th Street Bridge flyer, June 2021.
June 2021 flyer Download PDF document (1MB)

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.

The total project budget is $2.9 million. The project is funded by King County.

S 277th Street 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
    One 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 moves 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)
    Warning/advisory signs inform drivers of reduced lanes and reduced speed limit ahead.

  • Nearby roadways
    Signs notify drivers of upcoming and current project construction and construction impacts.

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


September 16 - second half of new culvert installed.
The second half of the new concrete box replacement culvert is installed on Sept. 16, 2021.

September 16 - second half of new culvert in place.
The second half of the new concrete box replacement culvert, in place on Sept. 16, 2021.

September 1 - first half of new culvert installed.
The first half of the new concrete box replacement culvert is installed on Sept. 1, 2021. Next, crews will bury this half, rebuild the road on top of it, and move both lanes of traffic over so that we can start work on the second half of this project.

September 1 - first half of new culvert installed.
The first section of the new culvert is lowered into place on September 1, 2021.

Work on the S 277th Street Bridge on August 11, 2021.
August 11, 2021 - Steel plates are used to cover the area under S 277th Street that has been excavated. The plates also cover a de-watering system that diverts Mullen Slough away from the construction zone.