Ames Lake Trestle Bridge No. 1320A Replacement Project

Project overview

This project replaces the 96-year-old Ames Lake Bridge with a wider structure and straighter bridge approaches. The improvements are designed to increase sight distance for drivers and provide a safe, unrestricted crossing for trucks and vehicles of all sizes. In addition, the new bridge will be designed to have less environmental impact on Ames Creek and the surrounding wetlands.

The new bridge will be built in the same location as the existing bridge and have no weight restrictions. The road will be closed for the duration of the new bridge construction and traffic must use a detour route. King County will return for a second open house in June 2022 and construction is set to begin in mid-2023. The new bridge should be complete in mid-2024.

Why is King County replacing the bridge?

The Ames Lake Trestle Bridge was built nearly 100 years ago and was originally designed with narrow lanes for much smaller vehicles compared with what we see on the road today. The bridge has a posted weight restriction for specific large trucks and specialized hauling vehicles. Replacing the bridge will provide a safer, unrestricted crossing for the community.

The original timber piles that support the deck are decaying. Over time, the poor condition of the piles could prohibit large trucks and emergency vehicles from crossing, which eventually would require the bridge to be shut down completely.

Project schedule

King County selected a preferred alternative for a replacement bridge, with construction projected to begin in 2023. The preliminary estimated total project cost is $15 million. This project is funded through the King County Capital Improvement Program and the Road Services Division Operating Budget.

Bridge access for residents and emergency vehicles will be maintained throughout construction. Construction activities will include demolition, concrete pouring, and crane lifts. After the new bridge is opened to traffic, crews will continue low impact restoration work including plantings and site clean-up.

Selected bridge design: Alternative 3B

Alternative 3B overview

• The roadway will be closed to traffic during demolition of the existing bridge and construction of the new bridge.

• Traffic will use a detour route for the duration of the new bridge construction.

• All project construction work will comply with terms and conditions set by our partner permitting agencies. King County will follow best practices to avoid negative environmental effects to the stream and other natural surroundings and keep the road open to traffic during construction.

Advantages

• EASIER TO BUILD: Locating new bridge in the same place as the existing bridge requires less ground shoring and leveling (grading). It also minimizes the size of retaining walls that will be required.

• PERMANENT BRIDGE FOUNDATION: Built outside of wetlands and Ames Creek.

• LOWEST CONSTRUCTION COST: Will offer significant cost savings due to the small project footprint and absence of a temporary bridge.

• LOWEST CONSTRUCTION DURATION: Much faster construction times with no temporary bridge, minimal ground shoring and leveling, and no adjacent traffic.

• BETTER WORKER SAFETY: Removing traffic near work zones creates a safer work environment.

• ENVIRONMENTALLY FRIENDLY: The smaller project footprint requires less tree removal and environmental disturbances.

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