A 30-year-old Lowell man was in critical condition after being thrown from his car during a crash involving a tractor-trailer Sunday morning, according to State Police. The man, who was not identified, was driving in the northbound lane of Interstate 495 in Boxborough just before 7 a.m., when his Toyota Corolla “made contact” with a tractor-trailer and flipped over, police said in a statement. The man was flown by helicopter to the University of Massachusetts Memorial Medical Center in Worcester with life-threatening injuries. State Police said troopers found the tractor-trailer and identified its owner but did not release the name. State Police spokesman Dustin Fitch said Sunday that no determination had been made about filing charges.Todd Feathers can be reached at firstname.lastname@example.org. Follow him on Twitter @ToddFeathers.