MOUNT VERNON, Wash. >> An Interstate 5 bridge over a river collapsed north of Seattle Thursday evening, dumping two vehicles into the water and sparking a rescue effort by boats and divers as three injured people were pulled from the chilly waterway.

Authorities said it appeared nobody was killed in the bridge failure that raised the question about the safety of aging spans and cut off the main route between Seattle and Canada.

“We don’t think anyone else went into the water,” said Marcus Deyerin, a spokesman for the Northwest Washington Incident Management Team. “At this point we’re optimistic.”  

A man and a woman were reported in stable condition with non-life-threatening injuries in the emergency room at Skagit Valley Hospital, hospital spokeswoman Kari Ranten said. Another man was reported in stable condition at United General Hospital in Sedro-Woolley, hospital CEO Greg Reed said. He said he didn’t know whether the man would be admitted.

Survivor Dan Sligh and his wife were driving their pickup truck when he said the  bridge disappeared before them in a “big puff of dust.”

“I hit the brakes and we went off the bridge,” Sligh told reporters from Skagit Valley Hospital, adding he “saw the water approaching … you hold on as tight as you can.”

Traffic along the heavily-travelled route could be impacted for some time.

“The I-5 corridor is totally disrupted,” said Gov. Jay Inslee, who went to the scene tonight.

He said work has already started to design detour, but state Transportation Secretary Lynn Peterson asked people to avoid I-5 in the area for the next several days.

Washington State Trooper Mark Francis said a portion of the four-lane bridge over the Skagit River collapsed about 7 p.m.

Jeremiah Thomas, a volunteer firefighter, said he was driving nearby when he caught something out of the side of his eye and turned to look.

“The bridge just went down, it crashed through the water,” he said. “It was really surreal.”

It was not known what caused the collapse of the bridge about 60 miles north of Seattle in Skagit County, but State Patrol detectives and the patrol’s commercial vehicle enforcement bureau troopers were talking late into the night to a commercial truck driver whose rig was believed to have struck the bridge.

“It appears the commercial vehicle made contact with the bridge,” Francis said. “Whether it was the cause” of the collapse or made contact as the bridge was falling “that will all come out in the wash. But it appears it hit the bridge.”

The four-lane bridge was about 50 feet above the water. Deyerin said it appeared that two vehicles – a car and a pickup with the travel trailer attached – fell into the river. He said the water depth was about 15 feet, and that the vehicles were half-visible in the water likely are resting on portions of the collapsed bridge.

Crowds of people lined the river to watch the scene unfold.

“It’s not something you see every day,” said Jimmy O’Connor, the owner of two local pizza restaurants who was driving on another bridge parallel to the one that collapsed. “People were starting to crawl out of their cars.”

He said he and his girlfriend were about 400 yards away on the Burlington Bridge when they heard “just a loud bang.”

“Then we looked over and saw the bridge was down in the water,” he said.

He pulled over and saw three vehicles in the water, including a camping trailer that landed upside-down, he said.

The bridge is not considered structurally deficient but is listed as being “functionally obsolete” – a category meaning that the design is outdated, such as having narrow shoulders and low clearance underneath, according to a database compiled by the Federal Highway Administration.

The bridge was built in 1955 and has a sufficiency rating of 57.4 out of 100, according to federal records. That is well below the statewide average rating of 80, according to an Associated Press analysis of federal data, but 759 bridges in the state have a lower sufficiency score.

According to a 2012 Skagit County Public Works Department report, 42 of the county’s 108 bridges are 50 years or older. The document says eight of the bridges are more than 70 years old and two are over 80.

Washington state was given a C in the American Society of Civil Engineers’ 2013 infrastructure report card and a C- when it came to the state’s bridges. The group said more than a quarter of Washington’s 7,840 bridges are considered structurally deficient of functionally obsolete.

Democratic Rep. Judy Clibborn, who leads the transportation committee in the state House, said the bridge wasn’t one that has been a focus for lawmakers.

“It is shocking that I-5 would have something happen like this,” she said.

Clibborn said the collapse will call attention to the issues facing bridges — especially the old bridge over the Columbia River that connects Vancouver and Portland, Ore.