A 16-year-old boy was critically injured when he was struck by a hit-and-run driver as he walked in Valencia Park on Sunday evening, San Diego police said. Police said the driver was heading west on Imperial Avenue near San Jacinto Drive around 8 p.m. when he or she struck the teen in the roadway. The driver left the scene, leaving the victim unconscious and bleeding in the middle of the street, San Diego police Officer John Buttle said. The victim was taken to a hospital with a head injury and is not expected to survive, police said. Traffic Division officers were investigating the collision. No other details were immediately available.