The bridge in 2013. (Rick Lund/Seattle Times via AP)

A bridge that collapsed in Washington state last year fell because an over-sized vehicle hit the structure, federal investigators said Tuesday.

The Interstate 5 bridge collapsed in May 2013, injuring three people and dumping vehicles into the Skagit River. An investigation conducted by the National Transportation Safety Board, which announced findings from its forthcoming report on the collapse, said that when an over-sized vehicle hit and damaged a portion of the bridge structure, it ultimately caused one of the spans to collapse.

This crash was not due to driver fatigue or weather conditions, investigators said; rather, it was caused by a vehicle that was too big to travel on these particular lanes on the bridge.

Had the over-sized vehicle moved one lane over before crossing the bridge, it’s likely the impact and the ensuing collapse would never have occurred, the NTSB said. The entire episode could have also been avoided had the trucking company considered the bridge’s clearance when planning the route, investigators determined.

Investigators recommend that the Federal Highway Administration develop a guide for states to use to prevent bridge strikes by vehicles that are too big, figuring out how to collect and share data on bridge strikes as well as reviewing what methods have reduced these bridge strikes. Authorities should also install better signage before structures that limit clearance over roadways, investigators said.