Modern-day bridges constructed with cables prevent incidents like the Interstate 5 bridge collapse over the Skagit River on Thursday, a retired B.C. engineer says.

"Cable is a modern design. All the cables give the structural support to hold the bridge up," Bob Bartar told CBC News. "This one doesn't have this. It's just got steel members, so if you remove one member ... the whole thing comes down."

Bartar was at a nearby casino when he heard about the bridge collapse and decided to take a look at the scene himself.

Three people were injured when two cars were dumped about 16 metres into the Skagit River at about 7 p.m. PT. All three are expected to recover.

The bridge, built in 1955, has been listed as "functionally obsolete" in a Federal Highway Administration database — a category meaning the design is outdated. According to the U.S. Ministry of Transportation, the bridge was inspected two months ago and passed all safety tests.

"It's the code of bridge design of that day, never designed for the traffic of today," Bartar said, comparing the bridge to a "Meccano" model construction set for children.

"When you put a Meccano set together, you screw all the parts together. You take out one screw and the whole thing falls down."

Bartar said all new bridges are now designed with cables, except bridges in more rural areas where the traffic is light.

Bridges inspected annually in Canada

The bridge over the Skagit River is about 130 kilometres south of Vancouver — about halfway between the Canadian border and Seattle — and the interstate is a major transportation route and the main link for Canadians driving between Vancouver and Seattle.

The U.S. National Transportation Safety Board is investigating the incident.

In B.C., there are 2,700 bridges ranging from modern cable bridges to old steel constructions built in the 1950s, similar to the collapsed bridge in Washington.

Kevin Baskin, the province's chief bridge engineer, says people shouldn't worry about the safety of B.C. bridges.

"We have robust systems in place for inspecting our bridges, making sure they are in good condition and safe," Baskin said.

"We also have robust procedures in place for issuing permits for vehicles that are going to go across our structures to make sure they can go safely across them."

Bridges are inspected annually in Canada, and Baskin says the large bridges are monitored by maintenance crews every day.

with files from CBC's Chad Pawson and Belle Puri