Urgences-Santé said the teen was rushed to hospital with injuries to his face and one side of his body.
Officials say he was conscious and alert, but called the injuries life-threatening.
It's not clear what kind of train was involved.
The accident and its investigation closed the Highway 20 West exit ramp at Cartier Boulevard and delayed train service through the late afternoon commute.
The Highway 20 West ramp re-opened just after 6 p.m.