A 22-year-old woman from Walpole died at the scene of a single-car crash on the southbound lanes of I-95 in Needham early Saturday, according to a statement from the State Police. Troopers responded to the incident at 2:15 a.m. The woman, identified as Sally C. White, was driving a 2004 Honda Civic and struck the side of a train bridge near Kendrick Street, before Exit 19B, the statement said. White was the only occupant of the vehicle. The State Police’s Framingham Barracks is investigating the cause of the fatal crash, said spokesman Dustin Fitch.