Boise X Connection Bridge #3055A sq̓ʷəlacucid* Replacement Project

Project overview

This project replaced the Boise X Connection Bridge #3055A located two miles south of Enumclaw, WA on SE Mud Mountain Road. This two-lane bridge was built in 1956 and had outlived its useful life. The previous bridge was weight restricted and could not safely support the weight of heavy fire engines and large commercial trucks.

Road Services removed the previous bridge and replaced it with a 67-foot-long, 34-foot-wide, two-lane reinforced concrete bridge in the same location. The new bridge does not have any weight restrictions. The project also improved sight distance for drivers by lessening the severity of a noticeable curve in the road approaching both directions of the bridge.

Project map

The Boise X bridge is located on SE Mud Mountain Road, south of Enumclaw, Washington. 

Larger view (490KB)

Why did King County replacing the bridge?

Replacing the bridge provided a safer, reliable crossing for the community.

The previous Boise X Connection Bridge was designed for much smaller vehicles compared with what we see on the road today. The bridge was nearly 70 years old. It had outlived its useful life and showed its age in the following ways:

• Original steel deck and steel girders were rusting.
• Creosote treated timber foundations were rotting.
• Lead-based paint was peeling off.
• The bridge was weight restricted—large trucks and other heavy vehicles could not this bridge.
• The bridge was too narrow for the size of cars and trucks that use the road.

The replacement bridge improves driver safety and the surrounding environment. This project also includes a public art installation, funded by King County's 1 Percent for Art program.

Safety improvements

• The new bridge is built to modern safety design standards.
• It is open to all vehicles, regardless of size or weight.
• The curves in the roadway approaching both ends of the bridge are slightly straighter to make it easier for drivers to see further ahead (improved sight distance).
• The new bridge has standard 11-foot-wide travel lanes, 6-foot-wide shoulders, and new bridge railings and guardrails on both sides.

Environmental improvements

As part of the bridge replacement crews working for King County Road Services:

• Removed decaying creosote timber support piles that leach toxic chemicals into the soil and water.
• Eliminated the source of lead paint currently peeling off the bridge and falling into the stream.
• Relocated the bridge supports further from the stream, giving the stream extra room to move.
• Installed large woody material and new streambed gravels to improve fish habitat.
• Removed invasive plants and restored the area with native shrubs and trees.

Public art installation

We are working with the Muckleshoot Indian Tribe to create and install new artwork on the bridge. Artist Lillianna Ramirez was selected through 4Culture, in partnership with the Muckleshoot Indian Tribe, and the design, now in development, was approved through their process. The artwork will feature images displayed on blades produced by our King County Sign Shop and will be installed by King County crews.

Timeline

Construction to replace the Boise X Connection Bridge began on June 1, 2026.

• Advertised project to contractors: Fall 2025
• Construction started: June 1, 2026
• Major work completed: November 7, 2026

Budget

The preliminary cost estimate for the project was $4.7 million. Funding sources include grants from the Federal Highway Administration (FHWA) and local King County matching funds.

Documents

• Public Notice and Opportunity to Comment - Boise X Connection Bridge No. 3055A Replacement Project (90KB). The Public Notice comment period was Friday, June 30 through Monday, July 17, 2023.

Photos

November 3, 2026: Crews working for King County planting native shrubbery along the Boise Creek at the project site. This is one of the few remaining activities of planned construction work and a major milestone for this project.

October 15, 2026: A newly striped section of the Foothills Trail crossing at SE Mud Mountain Road. 

October 14, 2026: Newly installed guardrail approaching the Boise X Connection bridge. 

October 5, 2026: SE Mud Mountain Road at the Boise X Connection Bridge has been paved. Crews also plan to install bridge rail on either side of the roadway to help prevent vehicles, pedestrians, and bicycles from falling into the creek in the event of a crash.

October 5, 2026: Crews are paving a section of SE Mud Mountain Road between SR 410 and 248th Avenue SE where the new bridge has been installed.

September 16, 2026: Newly installed rebar, which forms the foundation of the bridge approaches, where the bridge meets the roadway.

September 3. 2026: Salmon found in the newly re-connected Boise Creek, near the Boise X Connection Bridge. Crews diverted the stream in July 2026 to protect it from debris during construction.  

August 18, 2026: Crews oversee the crane carefully placing girders, the primary horizontal support structure for the bridge. Girder installation is a key milestone in bridge construction projects.

August 8, 2026: Crews are finalizing construction of the second bridge abutment, a wall on either side of the bridge that provides structural support. 

July 30, 2026: Anchored large log, which has been placed in the stream bed as part of stream bed restoration. This creates a natural stream bed for fish and other wildlife. 

July 21, 2026: One abutment wall will sit on either side of the bridge to provide structural support.

 July 9, 2026: Crews completing rebar work for the side walls of a bridge abutment.

July 7, 2026: Crews complete aqua damn installation to divert the stream and avoid contaminating it with debris. This is the first time this type of damn has been used on a King County Roads project. 

July 2, 2026: Rebar installation on the bridge abutment footing, or base. 

June 26, 2026: Crews are placing a thick fabric liner to prevent debris from weakening the structural stability of the bridge abutment. 

June 24, 2026: Crews are continuing structural excavation for a bridge abutment. 

June 18, 2026: Crews are setting up to pump water from a sump location so it can be treated before being released. 

June 16, 2026: Crews are completing structural excavation for the footing (base) of the abutment, a large structural support for the bridge structure on either side of the bridge. 

June 9, 2026: Contractor crews working for King County heating the existing metal bridge structure to make it easier to take apart. 

June 8, 2026: Crews are demolishing the existing Boise X 3055A Bridge. 

June 1, 2026: Construction to replace the Boise X Connection Bridge #3055A is underway. 

May 1, 2026: The Boise X Connection Bridge over Boise Creek was built in 1956. It got its name from an old, elevated Northern Pacific Railroad trestle that used to be adjacent to it. The blue netting shown above prevents birds from nesting ahead of construction.

May 1, 2026: Netting on the Boise X Connection #3055A Bridge prevents birds from nesting ahead of upcoming construction. 

September 2025 – A view of the bridge from the underside. Engineers indicated that daylight was visible from underneath the bridge deck. This discovery initiated protocol for Road Services staff to order materials, obtain necessary permits, and prepare notifications to the traveling public for lane restrictions on the bridge in order to make repairs. 

September 2025 – Maintenance crews and bridge engineers responded to a report of sinking and cracked pavement on the bridge deck. Engineers inspected both above and below the bridge to understand the cause of the sinking pavement.

April 2023 – A close-up look at the defect on the bridge deck. The bridge steel expanded as it rusted, which caused sinking and cracking of the pavement above.

April 2023 - Bridge engineers made repairs to the bridge deck in after receiving reports of the pavement beginning to dip. After removing a section of the asphalt, they identified the issue to be material decay. 

This is a photo of SE Mud Mountain Road approaching the bridge from the east. The curve in the road limits the ability to see traffic ahead, especially at night. The county will lessen the severity of this curve to improve sight distance for drivers. (Photo: March 2021)

July 2019 - The steel floor beams of the existing Boise X Connection Bridge are rusted and continue to age and deteriorate. King County will remove the entire bridge and replace it with a new concrete bridge.

July 2019 - The county has repaired and reinforced the decaying creosote timber bridge supports many times over the years. The creosote supports leach toxic chemicals into the environment. In addition, the large, jagged rocks and pieces of concrete shown above are not healthy habitat for fish and wildlife. (Photo: July 2019)

July 2019 - The existing Boise X Connection Bridge is restricted for heavy trucks and large fire engines. The new bridge will not have any weight limits. (Photo: July 2019)

Photo of Boise X Connection Bridge (foreground) when it first opened in 1956. The Northern Pacific Railroad trestle in the background was torn down in 1982.