Federal investigators ruled Tuesday that an oversize truck caused the collapse of an Interstate 5 bridge in Washington state by striking the overhead support trusses.
The steel-and-cement bridge, built in 1955, buckled and collapsed into the Skagit River on May 23, 2013, after the truck bumped several sections of the bridge with oversize drilling equipment.
Two following vehicles, one towing a camper, fell into the river. Three people were injured, but none killed.
The National Transportation Safety Board found the bridge had been hit repeatedly by oversize loads and that state permits for trucks didn't check whether they would fit under bridges along their proposed routes.
The board recommended:
• Better evaluation for permitting oversize trucks.
• More detailed information about bridge clearances for each lane of traffic.
• A prohibition against escort drivers using electronic devices such as cellphones.
• Better signs around bridges warning about clearances, especially when arched.
"Movement of oversized loads is a specialized operation that demands special precautions," said Christopher Hart, the board's acting chairman. "What this investigation uncovered were multiple gaps in multiple systems and repeated occurrences of similar bridge strikes."
The NTSB hearing came the same day President Obama gave a speech about the need for long-term bridge and highway funding. The House is also voting on a short-term extension of highway funding, but is at an impasse with the Senate over how to fund a four- to six-year extension.
In 2012, the Federal Highway Administration said 67,000 — or 11% — of the nation's 607,000 bridges were structurally deficient. That means the bridges are not unsafe, but must be closely monitored and inspected or repaired.
That percentage is little changed since 2007, when 12% of the nation's bridges were listed as structurally deficient and an Interstate 35 bridge collapsed in Minneapolis, which killed 13 people.
The I-5 accident blocked a major north-south artery between Seattle, 60 miles to the south, and Canada. An average of 71,000 vehicles a day crossed the bridge every day before the accident.
Just before the collapse, a 2010 Kenworth truck-tractor in combination with a 1997 Aspen flatbed trailer with an oversize load drove onto the bridge. The top of the load collided with the overhead portal and multiple braces on the far right side of the structure, NTSB said.
Two passenger vehicles — a southbound 2010 Dodge Ram pickup towing a 2009 Jayco camper trailer and a northbound 2013 Subaru XV Crosstrek — were on the bridge when it collapsed.
The driver of the oversize truck said it was 15 feet 9 inches tall, although federal investigators measured 15 feet 11 inches.
In either event, a state database of bridge clearances shows the arched bridge's lowest clearance on the right-hand lane was 14 feet 5 inches, according to investigators.
The bridge had been struck eight times by high loads in the year before August 2012, according to investigators.
Mullen Trucking, the Canadian company hauling the load, got a $10 permit on the Internet for the trip from Washington state that said "Route OK" and that the state agency "Does not guarantee height clearances."
"Everyone is pointing at everyone else," said Mark Rosekind, a board member.
The pole on an escort car driving ahead of the oversize truck struck the bridge several times, but the driver was distracted while talking on a cellphone, according to investigators.
But even if she had noticed, the truck was trailing by only 400 feet rather than the recommended 800 feet, so investigators said she wouldn't have had time to warn the truck driver.
The bridge was rebuilt with an 18-foot clearance across all four lanes of traffic, according to the board.