Page 1 \ 6 RCA Name Interstate 5 Skagit River Bridge Collapse Report Number WA12.684 Report Date 1/9/2014 Root Cause Analysis Report Problem Statement Focal Point Bridge Collapse When Start Date 5/22/2013 Start Time 7:05pm Unique Timing After oversized truck passed through outer lane Where Between Mount Vernon and Burlington in Washington State Skagit River Bridge on I-5 Actual I mpact Other Safety I-5 southbound closed for several weeks $0.00 Minor injuries $0.00 Bridge rebuilding $8,500,000.00 Actual I mpact Total: $8,500,000.00 Frequency times overall Frequency Notes Records indicate that this bridge has been struck multiple times. However, none of the previous strikes caused any significant damage. Potential I mpact Safety Potential fatalities to drivers crossing bridge. $0.00 Additional repair costs with increased damage. $0.00 Report and chart generated by Sologic s Causelink software. www.sologic.com
Report Summaries Page 2 \ 6 Executive Summary DISCLAIMER: the contents of this RCA report and chart were taken from the National Transportation Safety Board (NTSB)'s investigation report. Sologic did not participate in the investigation, or the development of the solutions for this analysis. On May 23, 2013, at approximately 7:05 pm PDT, a truck-tractor in combination with a flatbed semitrailer hauling an oversize load (the oversize vehicle) was traveling south on Interstate 5 (I-5) near Mount Vernon, Washington. The oversize vehicle had a permit for the route of travel and was being led by a pilot/escort vehicle. As the oversize vehicle traveled across the I-5 bridge above the Skagit River, it struck the bridge, damaging its structure. As a result of contact damage to the bridge s truss structure, span 8 of the 12-span bridge collapsed into the Skagit River. Two passenger vehicles fell into the river. Two other vehicles were also damaged during the event. Eight vehicle occupants were involved in the bridge span collapse; three received minor injuries and five were uninjured. In order to prevent further collapses on this bridge, the bridge was rebuilt with an 18-foot clearance over all lanes and recommend that the Federal Highway Administration develop a guide for eliminating or reducing bridge strikes. Cause and Effect Summary The bridge collapse was caused by an oversized truck striking multiple bridge trusses. The truck struck the trusses because the outside lane was 4.45 meters tall, the truck was 4.5 meters tall and the truck was traveling in the outside lane (the truck was supposed to travel in the inside lane). The truck was in the outside lane because he was unaware his load was taller than the bridge in that lane. He was unaware because: 1) There were no signs indicating the lane requirements/heights, 2) There was no indication of the height restriction in the permit for the trucking company, and 3) No one warned him. The escort car did not warn the driver of the clearance issue because the escort driver was talking on his cell phone and did not notice the clearance pole striking the bridge. There was no mention of the lane heights in the permit because Washington State truck permits are not required to verify that trucks will fit under bridges. The driver was driving in the outside lane because he moved over to let faster traffic pass.
Solutions Page 3 \ 6 ID 1 Label Solution Cause Note Description Bridge rebuilt with 18 foot clearance across all lanes Outside lane height = 4.45m Assigned Criteria Pass Due Status Completed Term $8,500,000.00 2 Solution Ask the Federal Highway Administration to develop a guide for states on how to prevent bridge strikes by vehicles, including collecting and sharing data, and evaluating and reviewing bridge strike countermeasures taken by states. Cause Note Assigned Due Term Criteria Status Not Checked Identified
Evidence Page 4 \ 6 ID Label Description 1 Evidence NTSB Investigation Report Truck impacted truss and multiple braces Sufficient force to fracture bridge Fracture-critical design Through truss bridge design Truck height = 4.8m Outside lane height = 4.45m Speed of truck approx. 60 mph Truck traveling in outside lane Driver unaware inside lane designed for taller vehicles Moved to right lane to let cars pass State truck permits don't verify that trucks will fit under bridges No warning signs for clearance height Sign not required by law for bridges over 14 feet (4.3m) 14 feet (4.3 m) is the normal legal height limit Mass of truck 88,700 lbs No one informed the driver about lane vs. height http://www.ntsb.gov/investigations/reports_highway.html Document 2 Evidence Wikipedia Common bridge design when bridge was built in 1955 Failure of essential part can cause overload/collapse http://en.wikipedia.org/wiki/i-5_skagit_river_bridge_collapse Web 3 Evidence USA Today news story Escort car did not communicate clearance issue
Pole designed to provide clearance warning Pole on escort car struck bridge several times Driver did not notice Driver distracted - talking on cell phone DOT automatically issues permits online Page 5 \ 6 http://www.usatoday.com/story/news/nation/2014/07/15/ntsb-bridge-collapse-inters tate-5-washington-state/12671469/ Document 6 Evidence Bridge rebuilding cost data from WSDOT website http://www.wsdot.wa.gov/projects/i5/skagitriverbridgereplacement/ Web
Notes Page 6 \ 6 ID 1 Label Note Description This steel through-truss bridge has a "fracture-critical" design with non-redundant loadbearing beams and joints that are each essential to the whole structure staying intact. An initial failure (perhaps by cracking) of a single essential part can sometimes overload other parts and make them fail, which quickly triggers a chain reaction of even more failures and causes the entire bridge span to collapse. Cause Fracture-critical design 2 Note In WA, only overcrossings of less than 14 ft (4.3m) are required to have advance postings of height restrictions. Cause Sign not required by law for bridges over 14 feet (4.3m) 3 Note Large vehicles should be in inside lane (5.2 m high) Cause Truck traveling in outside lane 4 Note Clearance pole struck bridge, per NTSB report Cause Driver did not notice
Chart Legend Transitory Report and chart generated by Sologic s Causelink software. State truck permits don't verify that trucks will fit under bridges DOT automatically issues permits online Non-transitory Omission - Transitory Omission - Non-transitory Focal Point www.sologic.com Driver unaware inside lane designed for taller vehicles No warning signs for clearance height Sign not required by law for bridges over 14 feet (4.3m) 14 feet (4.3 m) is the normal legal height limit Solution Implemented No one informed the driver about lane vs. height Truck traveling in outside lane Moved to right lane to let cars pass Escort car did not communicate clearance issue Driver did not notice Driver distracted - talking on cell phone Truck impacted truss and multiple braces Outside lane height = 4.45m Connects to: b Through truss bridge design Solutions Bridge rebuilt with 18 foot clearance across all lanes Criteria Pass Status Completed Bridge Collapse Truck height = 4.8m Mass of truck 88,700 lbs Sufficient force to fracture bridge Speed of truck approx. 60 mph Through truss bridge design Common bridge design when bridge was built in 1955 Fracture-critical design b Failure of essential part can cause overload/collapse