Tim Gordon was driving his truck Thursday afternoon northbound on Highway 27, north of Highway 401, when he saw it all unfold.
More importantly, his dashboard camera caught it all on video: a car performing an illegal U-turn, cutting off another vehicle in the fast lane — what Gordon calls "the hammer lane" — causing that vehicle to roll over.
"I don't think [the driver] was prepared for the guy to cut in front of him, and clipped him at I think pretty much full speed and then lost control, rolled it into the right ditch," Gordon told CBC News Thursday evening.
Gordon stopped to help the driver and said he seemed to be all right.
"I did administer some medical aid to the gentleman who at that time was able to get out of his car. I think the ... front airbag punched him in the head and he had a bloody nose ... I think he was OK, he was just in shock."
Gordon said it took about 10 minutes for paramedics to arrive.
"It's amazing no-one was killed," he said, adding that it's a reminder that drivers have to stay alert.
"Some of the most unexpected things can happen and will happen and you have to be prepared for anything at any time on Toronto's roads."
Gordon also said dashboard cameras are an important safety tool for motorists, and an investigative tool for police.
"I highly recommend people invest in a good quality dashcam, not a cheap one, because it helps the police evaluate drivers and easily deconstruct collision scenes."