This is breaking news, and this blog post will be out of date.
The Interstate 5 bridge over the Skagit River has collapsed near Mount Vernon, Washington. A map shows where the incident happened, about half way between Seattle and the Canadian border.
As of this writing there are no confirmed details about the cause of the bridge collapse. The Seattle Times says it may have been because an oversized truck hit the bridge with its load. Three people were rescued from the water with minor injuries.
Scanner, via Broadcastify: Skagit County Police and Fire. 4400+ listeners at 8:19 p.m. 5/23/13. This is the initial police response, via Soundcloud and Alertpage.
Skagit Valley-News: Reports: Bridge collapses between Mount Vernon, Burlington
The I-5 Skagit River Bridge is a through-truss bridge that was built in 1955, according to the website Bridgehunter.com. It is the same basic type of design of the Interstate 5 Bridge over the Columbia River in Vancouver, according to the site.
Associated Press: I-5 bridge collapses in NW Wash.; people in water.
Bridgehunter.com: I-5 Skagit River Bridge. Includes maps and photos of bridge.
National Bridge Inventory Database details follow, from NationalBridges.com. The structural evaluation is "Somewhat better than minimum adequacy to tolerate being left in place as is".
|Place Name:||Mount Vernon|
|NBI Structure Number:||0004794A0000000|
|Route Sign Prefix:||Interstate|
|Feature Intersected:||SKAGIT RIVER|
|Location:||0.7 N JCT SR 538|
|RecordType:||Roadway is carried ON the structure|
|Level of Service:||Mainline roadway|
|Owner:||State Highway Agency|
|Highway Agency District:||01|
|Maintenance Responsibility:||State Highway Agency|
|Functional Class:||Principal Arterial – Interstate, Urban|
|Service On Bridge:||Highway|
|Service Under Bridge:||Highway-waterway|
|Latitude:||48 26 35.80 N|
|Longitude:||122 20 27.90 W|
|Design Construction:||Truss – Thru|
|Approach Material Design:||Concrete continuous|
|Approach Design Construction:||Tee Beam|
|Structure Length (m):||338.9|
|Navigation Vertical Clearance (m):||2.4|
|Approach Roadway Width (m):||21.9|
|Lanes on Structure:||4|
|Lanes under Structure:||4|
|Average Daily Traffic:||70925|
|Year of Average Daily Traffic:||2010|
|Design Load:||MS 18|
|Scour:||Bridge foundations determined to be stable for assessed or calculated scour condition.|
|Bridge Railings:||Meet currently acceptable standards.|
|Historical Significance:||Bridge is not eligible for the National Register of Historic Places.|
|# of Spans in Main Structure:||4|
|# of Spans in Approach Structures:||8|
|Transitions:||Does not meet currently acceptable standards.|
|Approach Guardrail:||Meets currently acceptable standards.|
|Approach Guardrail Ends:||Not Applicable|
|Navigation Control:||Navigation control on waterawy (bridge permit required).|
|Navigation Horizontal Clearance (m):||33.5|
|Structure Open?:||Open, no restrictions|
|Structural Evaluation:||Somewhat better than minimum adequacy to tolerate being left in place as is|
|Sufficiency Rating (%):||57.4|
News coverage – this may change as time progresses: