County starts design on repairs to Tolt Hill Bridge; no decision yet on opening bridge to limited traffic

Closed since the evening of June 16 for safety reasons, the Tolt Hill Bridge near Carnation is still under review for needed repairs and a possible re-opening to limited traffic.

King County, owner of the bridge, is consulting with the Washington State Department of Transportation bridge experts, the Federal Highway Administration and a design engineering firm to discuss next steps for the bridge.

The county’s consultant design engineering firm is developing a repair design, reviewing the new federal methodology for determining the load a bridge can carry, and will work with a design expert who specializes in this type of bridge (steel truss design). A contractor will also be hired to provide a review of the project design.

Updates will be posted on the Tolt Hill Bridge Emergency Repairs webpage.

The bridge was closed following a series of inspections in recent months, prompted by a 2014 change from the Federal Highway Administration in how bridges were rated for loads. Engineers found discrepancies between the actual measurements taken on the bridge and the original designs and determined that the design firm had mistakenly transferred the wrong minimum measurements from the design to the plans. The problem was not caught when the $17 million bridge opened in 2008, because the inspection of the bridge was made against the faulty plan, not the correct original designs.