A driver talks on his cell phone. (MIKE DREW/QMI AGENCY FILE)

TORONTO — Talking on a cellphone while making a left-hand turn can be a deadly mistake, according to Toronto researchers.

Neurologist Tom Schweizer, a researcher at St. Michael’s Hospital, found that talking on a cellphone — even a hands-free unit — while making a left could be the most dangerous thing motorists do on the road.

“Hands-free does not mean brains-free,” Schweizer said.

Most serious traffic accidents happen at busy intersections where drivers are turning left.

Researchers, led by Schweizer — director of St. Michael’s Neuroscience Research Program — used a high-powered MRI machine to test healthy, young drivers operating a driving simulator equipped with a steering wheel, brake pedal and accelerator. They discovered that making a left required far more brain activation than when a motorist drives on a straight road.

“You have to look at oncoming traffic, pedestrians and lights, and co-ordinate all that. Add talking on a cellphone, and your visual area shuts down significantly, which obviously is key to performing the maneuver.”