A man was critically injured yesterday after crashing into the back of a tractor-trailer on the New York State Thruway during the morning commute. The driver appeared to have struck the truck while it was stopped on the shoulder. The driver had to be extricated from the vehicle. He was then taken to a nearby field and airlifted to Westchester Medical Center with life-threatening injuries. The driver of the truck was reportedly uninjured. The crash is under investigation.