A pedestrian sustained critical injuries Monday night when he was hit by a car that fled the scene in Chelsea, police said. The 57-year-old victim was crossing Washington Avenue near Carmel Street just before 7:30 p.m. when a sedan hit him and sped away, Chelsea police said in a statement. The victim was taken by ambulance to Massachusetts General Hospital, police said. Witnesses told police the car was a dark, possibly green, two-door sedan that had front-end and possible windshield damage, the statement said. Police are asking anyone with information to call 617-466-4829.Nicholas Jacques can be reached at firstname.lastname@example.org.