News from King County Department of Transportation
Release date:  July 10, 2008

Traffic alert for Mt. Si Bridge near North Bend

Motorists traveling on Mt. Si Road will encounter changing construction conditions starting Saturday, July 12, as King County continues its project to replace the Mt. Si Bridge over the Middle Fork of the Snoqualmie River near North Bend.

The biggest change for motorists is in the late afternoon on Monday, July 28 when traffic is diverted to the new bridge. At that point, it will still be several months before the bridge project is completely finished.

The King County Road Services Division is replacing the existing 94-year-old Mt. Si Bridge with a new span that has improved horizontal and vertical alignment and separate lanes for motorists, bicyclists, and pedestrians. The new alignment and increased vertical clearance will improve visibility for drivers approaching and leaving the bridge. It will also be wider than the existing bridge, with an eight-foot-wide shoulder on the west side and a four-foot shoulder and six-foot sidewalk on the east side. It is longer than the existing bridge to avoid interfering with the river's natural width.

The old and new bridges are positioned close together, and the county needs to divert traffic to the new bridge so it can dismantle the old bridge and finish constructing the north approach. Crews will be working on both bridges simultaneously. Motorists are urged to drive with caution through the construction area, and obey the instructions of flaggers.

The current construction schedule includes these key dates:

• Saturday, July 12 – The bridge approaches on the existing Mt. Si Road will be pulverized, and motorists should use extreme caution while driving on the loose gravel.
• Wednesday & Thursday, July 23-24 – The new bridge approaches will be paved.
• Monday, July 28 at 5 p.m. – Traffic is switched over to the new roadway and new bridge. Motorists should continue to drive carefully through the construction area.

The new bridge will be completed later this fall.