News from King County Department of Transportation
Release date:  May 30, 2008

Tolt Bridge – May 30, 2008
Fact Sheet

Background and History

• The old bridge was built in 1922 over the Snoqualmie River on Northeast Tolt Hill Road west of the city of Carnation. It was a steel Pratt through truss of the Parker sub-type, one of two remaining bridges in King County with fully riveted connections. The truss was 200 feet long while the bridge was 696 feet long and 19 feet wide. Since the 1980s, the bridge has been posted for one legal load at a time due to its narrow width and deteriorating structure.
  
• Construction of a replacement bridge began in June 2006. The new bridge opens for public use on May 30, 2008. Once it opens, the old bridge will be demolished during summer of 2008.
  
• The King County Department of Transportation Road Services Division built the new bridge with funding from federal Bridge Replacement Advisory Committee (BRAC) grants. The grants were administered by the Washington State Department of Transportation.
  
• Total project cost: $28.2 million; includes $22.7 million in construction and inspection costs and $5.5 million in study, design, land acquisition, environmental review and permitting costs.

Construction Scope

• The old bridge was replaced due to its deteriorated structural condition and its non-compliant bridge width. It was too weak for heavy trucks and had narrow traffic lanes, no shoulders, and substandard vertical and horizontal curves with limited sight lines. It would also likely collapse in an earthquake due to its rusting steel, rotting timbers, and a deteriorating concrete deck beam.
  
• The new bridge is located on a new alignment, approximately 165 feet upstream of the old bridge, and reflects the old span’s historic appearance.
  
• The new bridge is approximately 1,000 feet long consisting of two 300-foot long steel trussed spans, a short approach span on the west side, and three 120-foot long concrete girder spans on the east side of the river. It has the longest single span in the county’s 185-bridge inventory. The new bridge includes two 12-foot-wide travel lanes, two 8-foot-wide shoulders, and barriers on each side. Bicyclists and pedestrians will share the shoulders. The new bridge is designed to withstand major earthquakes and floods.
  
• The project also features: a newly realigned intersection for West Snoqualmie River Road and Northeast Tolt Hill Road; relocated boat launch access; relocated utilities to accommodate future needs; a new box culvert to facilitate fish passage; and stormwater facilities.
  
• When the old bridge – including approaches and abutments – is removed, the site will be restored with native vegetation or drainage enhancements. A portion of the old bridge may be salvaged, sandblasted, and relocated to a local park.

Environmental Aspects

• Mitigation was provided for temporary construction-related activities, as well as long-term impacts to habitats in the vicinity of the bridge that support populations of Pacific salmon and wildlife including chinook salmon, bull trout and bald eagles.
  
• The bridge piers were installed with temporary trestles to minimize impact to the wetlands and the Snoqualmie River, a Chinook salmon bearing stream.
  
• A special “bubble curtain” was successfully used during pile driving within the river to attenuate noise impacts to juvenile fish. No injured fish were recorded during or after the pile driving events.
  
• Bridge supports were placed outside the Ordinary High Water Mark (OHWM) of the Snoqualmie River and its tributaries to minimize impact on the flood carrying capacity of the stream.
  
• Additional fill in the floodway was mitigated by off-site excavation to ensure no net loss to floodway storage.
  
• A new box culvert at Tributary 2, south of the bridge, mitigated impacts to fish by replacing a non-fish passable pipe and enhanced riparian vegetation.
  
• A stormwater wetland facility on the west side of the river and a bioswale on the east side of the river mitigated water quality impacts from pavement runoff that was previously untreated.
  
• Impacts to wetland, stream and their buffers were mitigated on-site on both sides of the Snoqualmie River to provide forage and nesting habitat for wildlife.
  
• Benefits from the removal of the old bridge include the elimination of lead-based paint debris falling into the Snoqualmie River and removal of flood channel constrictions caused by the old bridge piers and abutments.

Project Team

• Project Sponsor – King County Department of Transportation, Road Services Division, Engineering Services Section
• Design Consultant – Lin & Associates, Inc.
• Contractor – Wilder Construction Inc.

Key Partners and Stakeholders

• Federal Highways Administration
• Washington State Department of Transportation
• King County Department of Natural Resources and Parks (DNRP)
• City of Carnation
• Puget Sound Energy
• Comcast
• CenturyTel
• Tolt Historical Society
• Snoqualmie Tribe

Permit and Approval Agencies

• King County Department of Development & Environmental Services
• King County Department of Natural Resources and Parks
• King County Historic Preservation Program
• King County Landmarks Commission
• Washington State Office of Archaeology and Historic Preservation
• Washington State Department of Transportation
• Washington Department of Fish & Wildlife
• Washington State Department of Ecology
• Washington State Department of Natural Resources
• National Marine Fisheries Services
• U.S. Fish & Wildlife Service
• U.S. Army Corps of Engineers
• Federal Highways Administration