An investigation is underway to determine how a City of Winnipeg dump truck crashed into a railway bridge, tearing the box off the back of the truck on Monday.

The truck hit the underside of a CP Rail bridge on McPhillips Street, between Logan Avenue and Jarvis Avenue, just before 8 a.m. CT.

The torn-away box ended up leaning against the bridge, blocking traffic for much of the morning.

Police set up barricades in the area and rerouted traffic down Henry Avenue.

The truck was removed shortly before 11 a.m. and all lanes of McPhillips have been re-opened to traffic.

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The bed portion of a dump truck sits against a railway overpass on McPhillips Avenue on Monday. (Trevor Dineen/CBC)

The truck driver was taken to hospital in stable condition for observation.

CP Rail said structures experts have examined the bridge and deemed it safe to continue to run the trains across.

"It was not until after the bridge went through a thorough inspection to ensure it met our safety requirements that trains were allowed to move again over the structure," CP Rail spokesman Ed Greenberg told CBC News.

Greenberg said the railway company is not responsible for signage on the bridge, or for installing warning lights on it.

CP Rail is only responsible for the rail portion of the structure, he said.