The collapse of an interstate highway bridge that was struck by a truck carrying an oversize load was ultimately caused by a series of deficiencies in a system intended to safeguard the passage of oversized loads over Washington state's roadways, the National Transportation Safety Board determined in a meeting earlier this week.
On May 23, 2013, at about 7:05 p.m. PDT, a heavy truck operated by the Canadian firm of Mullen Trucking LP, was traveling southbound on I-5 when the oversize load it was carrying struck the top of a bridge spanning the Skagit River near Mt. Vernon, Wash. Seconds later, the damage caused a span of the bridge to collapse. Two passenger vehicles and a camper-trailer fell into the river, and two other vehicles were damaged. None of the eight vehicle occupants involved in the bridge collapse was seriously injured.
The deficiencies cited by the NTSB included the failure of the driver of the pilot/escort vehicle to perform basic safety functions, inadequate route planning by the trucking company, Washington State's inadequate permitting process, and the lack of low-clearance warning signs for the bridge.
Mullen had hired another company, G&T Crawlers, to operate a pilot/escort vehicle as required by state law for the trip from the Canadian border to the truck's destination, the port of Vancouver, Wash. The truck followed the pilot/escort vehicle, which was equipped with a height pole intended to verify clearance from obstructions for the oversize load.
In the 30 minutes leading up to the accident, the driver of the pilot vehicle had used a hands-free mobile phone to engage in five calls, including the one that she was on when the truck struck the bridge. An off-duty commercial truck driver traveling near the pilot vehicle said he saw the height pole strike four or five bridge elements.
Although the trucking company had obtained a permit for the trip, it failed to check and plan accordingly for the low clearances encountered along the route. As the truck approached the bridge, it was traveling in the right lane where the clearance was lowest due to the arc design of the support brace. Investigators said that had the truck been in the left lane, where the vertical clearance was greater, the oversize load would have cleared the bridge.
The NTSB called for changes in the permitting process used by Washington State Department of Transportation to authorize movements of oversize loads on its roadways.
The NTSB also said that the lack of warning signs was a concern since WSDOT did not have any low-clearance signs by the interstate highway bridge to warn drivers of the height restrictions. Washington state has 22 bridges on its interstate system with a similar design as the Skagit River Bridge, and none has low-clearance signs or gives any indications of the lane oversize vehicles should use.
“We appreciate the work of the NTSB and its recommendations,” said Washington Secretary of Transportation Lynn Peterson in a statement. “WSDOT has already begun acting on NTSB’s recommendations for improving access to data for the freight industry to better plan travel routes of oversized loads. We will work to enact all of its recommendations and will continue to work closely with the Washington State Legislature and freight industry on the recommendations that require legislative action.”
A synopsis of the NTSB report, including probable cause, findings, and a complete list of the safety recommendations, is available at http://go.usa.gov/Xugm.
