It happened a little after 1 a.m. Sunday, in the eastbound lanes.
RCMP Cpl. Quentin Frewing says police were conducting a road stop on the bridge to check motorists for drugs and alcohol when he noticed something odd going on.
"There was a vehicle that pulled over and put their hazard lights on. I thought they were avoiding the road block, so I got in my police car and swung around and came roaring up here, and it turns out there was a collision," said Frewing.
Frewing said a driver struck a line of cars stopped for the road block, causing a rear-end chain reaction involving three other cars.
"The driver, obviously, was not paying attention and rear ended the vehicle. It is possible they fell asleep," said Frewing. "I administered a roadside screening device and the driver was not impaired."
One man was taken to hospital after first responders carefully removed him from the first car that was struck.
Frewing said the patient was conscious, speaking and complaining about back pain. Paramedics kept him immobile and carefully loaded him onto a stretcher.
The other drivers were a little shaken up, but uninjured, according to Frewing.
Frewing said the driver accused of causing the crash was issued a ticket for driving without due care and attention.