Commuters who regularly travel between Sammamish and Fall City will have to look for an alternate route for the next three months.

The King County Road Services Division began construction Aug. 16 to replace the more than 60-year-old Patterson Creek Bridge located on Southeast Duthie Hill Road, near State Route 202.

Work on the narrow two-lane bridge is expected to run through Nov. 16.

The bridge, located between Sammamish and Fall City, was built in 1951 and its creosote-treated timber supports are decaying.

When complete, the replacement bridge will increase safety and improve traffic flow for the more than 5,200 vehicles that use the road daily.

The current bridge is 24 feet wide with narrow shoulders, and the new bridge will be 38 feet wide with two 11-foot-wide traffic lanes and 8-foot-wide shoulders.

A posted detour will direct drivers to Old Southeast Issaquah-Fall City Road.MidMountain Contractors Inc. is allowed to work daytime hours seven days a week.

Support pilings for the new bridge are scheduled to be installed later this month. Approaches to the bridge will be built on Geofoam – rigid light-weight Styrofoam – that will better support the roadway across the weak peat soils and avoid settling.

The project cost is $3.1 million.