News from King County Department of Transportation
Release date:  June 26, 2006

County begins construction of new Tolt Bridge

Clearing starts this week on west side of Snoqualmie River near Carnation

Preliminary clearing and grading begins this week on King County’s biggest road project of the year – the construction of a new Tolt Bridge. Actual construction activities will start after the Fourth of July holiday.

The new $27.5 million bridge will span the Snoqualmie River just west of Carnation and approximately 165 feet upstream from the current historic bridge on Northeast Tolt Hill Road. The new bridge will be wider, safer for motorists and pedestrians, plus is designed to reduce river flooding in that location.

This is the largest construction project for the King County Road Services since the completion of the new Elliott Bridge in 2005. Construction of the new Tolt Bridge is expected to last for up to two years. The Roads Division is staging the construction to avoid fish-spawning seasons and to minimize traffic disruptions for local residents.

One of the goals is to keep Northeast Tolt Hill Road open to traffic as much as possible throughout construction. Motorists can expect a two-week closure from July 5-19 this summer, and then another in the spring of 2008. In addition, access to the boat launch near the bridge will be closed from July 12 to August 9. There could also be occasional short closures for maintenance work on the old bridge, but otherwise the road should remain open throughout the majority of the construction period.

The first activity at the project site will be removal of brush and some trees this week on the west side of the bridge near the intersection of Northeast Tolt Hill Road and West Snoqualmie River Road Northeast. This will set the stage for realignment of that intersection and construction of a temporary trestle that will allow construction equipment to get close to the river without damaging the sensitive areas.

All that set-up must be completed by Sept. 15 of this year to meet the state’s window for work in and around salmon-bearing waterways.

“We want construction to keep moving throughout the two-year length of the project, which will be challenging because of all the environmental considerations,” said Managing Engineer Rose LeSmith. “We have a lot of fish windows to work around on this project.”

Early next month, the contractor will be placing a huge order for the steel that will go into the new bridge. The order is so large that project managers estimate it will take nine months to fabricate and then deliver to the site.

The county has been working to replace the Tolt Bridge for many years. Extra time was needed to gather funding for the costly project, negotiate agreements with numerous agencies on environmental issues, and to address residents’ concerns about the design of a bridge that would replace a community landmark.

The existing bridge is more than 80 years old and needs frequent maintenance, often requiring traffic closures. It has limited sight distance, a narrow roadway, and restricted weight limits. It also does not meet current seismic, safety, or roadway design standards. In addition to constructing a modern bridge, this project will widen and realign Northeast Tolt Hill Road both east and west of the new bridge to increase sight distance and safety.

The plans call for a 970-foot-long bridge made up of two 300-foot-long trusses over the west side of the river and the river itself, and a concrete girder section on the east side. The twin trusses will echo the historic look of the existing bridge. The new bridge will have a cast-in-place, 40-foot-wide concrete deck supported by six double-column concrete piers.

Because of its proximity to the Snoqualmie River and three of its tributaries, the project includes significant environmental mitigation work. The bridge supports will be placed outside the stream channel to reduce flooding and avoid harming fish habitat along the river. The county will plant trees and shrubs to reduce the project's impact on adjoining wetlands and buffers. And, it will also construct a water quality pond and a bioswale to treat stormwater runoff.

An eight-foot-wide shoulder for pedestrians and bicyclists will be added on both sides of Northeast Tolt Hill Road and the bridge. An open-rail type barrier will be built on both sides of the new bridge for safety.