Low Vertical Clearance Truss Bridges: Risk Assessment and Retrofit Mitigation Study

The Washington State Department of Transportation (WSDOT) has over 60 steel truss bridges in
its inventory with vertical clearances less than the minimum 16’-6” required for new bridges.
This study evaluates the risks of oversized vehicle impacts to existing truss bridges with low
vertical clearances. The Skagit River Bridge SR5/712 was hit by an oversized load on May 23rd,
2013 resulting in a catastrophic collapse. At the time of the collapse, the Skagit River Bridge had
less than the minimum vertical clearance. WSDOT undertook this study to evaluate the risks of a
similar occurrence happening and to evaluate potential mitigation schemes. Scoping level
construction estimates for each scheme were then developed for all structures with substandard
vertical clearance. All bridges were prioritized based on risk using a range of evaluation criteria.
The goal and eventual purpose of the study is to be used as an asset management tool for
programming future retrofit projects and for procuring the necessary funding.

Publication Date: 
Friday, November 10, 2017
Publication Number: 
WA-RD 876.1
Last modified: 
01/17/2018 - 14:20
Geoffrey D. Swett, Gary Bedi
Washington (State). Dept. of Transportation. Bridge and Structures Office.
Number of Pages: 
Truss bridges, Highway bridges, Height, High risk locations, Truck crashes, Oversize loads, Crash risk forecasting, Hazard evaluation, Crashes, Hazard mitigation, Retrofitting, Recommendations.