Slough River Bridge 8.8

Slough River Bridge (Portland, OR)

Type: Swing Span, Through Truss
Location: Portland, OR
Owner: BNSF Railway


The Sough River Bridge crosses a distributary of the Columbia River known as North Portland Harbor and historically as the Oregon Slough and is a critical part of BNSF’s freight infrastructure as well as providing an essential passage for Columbia River marine traffic.

Due to the age and general condition of the bridge’s electrical systems and the desire to maintain its long-term reliability, Stafford Bandlow Engineering, A Division of WJE (SBE) was contracted to design the replacement and the upgrading of the aging bridge electrical systems, replace the failing electric service submarine cable, and design a backup automatic standby generator.

The design changes and additions to the electric service include the construction of a new electric service compound containing a standby generator and automatic transfer switch, a new submarine cable installation, and a new power slip ring arrangement at the center bearing to transition power between the pivot pier and the moving structure.

The bridge drive and control system design consist of the existing of the span drive motor with a variable frequency drive and squirrel cage induction motor. This combination has the capability of operating the bridge at infinitely variable speed with torque control and dynamic braking. The existing relay logic and operator’s control console replacement design consists of a modern programmable logic controller (PLC) with built-in SCADA and diagnostic functionality, a new streamlined and simplistic operators control station with an HMI providing status, alarm and control functionality.

Once implemented these changes and bridge electrical system enhancements will provide the bridge with a reliable electrical operating system for at least the next 30-years with minimal maintenance.