Projects

Project Description

This project consisted of constructing a new overpass on Old Highway 99 over the BNSF railroad tracks. The Burlington Northern Overpass is a vital part of both the County and state transportation system. Due to the importance of maintaining this arterial for the local freight community and for commuters, Skagit County chose to replace the existing timber and steel truss structure that was constructed in 1936. The existing structure was both structurally deficient and functionally obsolete, with a National Bridge Inventory System (NBIS) sufficiency rating 3 out of 100, which put this bridge as one of the top 5 worst rated bridges within Washington State.

The new overpass is comprised of SEW (structural earth wall) approaches nearly 1600 feet in length up to the rail tracks; and then a 395 feet long, 3 span prestressed concrete girder bridge founded on 6- and 8-foot diameter drilled shafts. Soft soils in the vicinity of the bridge alignment required ground improvements via the stone column method prior to construction of the SEW approaches. All structure work required strict coordination with the BNSF railway to ensure safety and minimize impacts on railway activities.