It's still not known what caused a single vehicle crash on the westbound 401 near Highway 37 during the noon hour on Tuesday. 

The collision resulted in a tractor trailer hauling a fifth wheeler going into the ditch and flipping over onto its roof. 

OPP say two people inside the tractor-trailer had to be extricated with help from fire crews who also attended the scene. 

The pair were taken by ambulance as a precaution to hospital with minor injuries. 

The affected section of the westbound 401 was closed for a couple of hours for crews to clear the scene of that crash.