A single-vehicle collision on Highway 401 was expected to block all but one eastbound lane between Guelph and Milton until around 4 p.m. Monday.

The collision occurred around 1 p.m. between the Highway 6 South and Guelph Line exits.

According to the Ontario Provincial Police, it involved a transport truck that hit a guardrail and flipped onto its side while in a construction zone, causing significant damage.

The truck’s driver was not hurt, and it was essentially empty of cargo at the time of the collision.

However, damage to the truck meant that it would take some time for crews to figure out how to upright it and get it off the highway.

As of 2 p.m., traffic was getting by on the left shoulder, but all normal traffic lanes were blocked by the aftermath of the collision.

GO Transit said a number of its bus routes could be delayed by as much as 30 minutes due to the closure.