SEATTLE - Washington State Patrol investigators are trying to determine what caused a fatal head-on collision between a Dodge Caravan and a Chevy pickup on SR 99 late Friday night. The pickup was travelling southbound on West Marginal Way South, just south of 14th Avenue South, when the truck left the road, State Patrol reported. The Chevy then crashed through a chain link fence, and into the northbound lanes pf SR 99, hitting the minivan head on. The driver of the minivan was killed; she's been identified as Vickey Tilson, 51, from Seattle. Two passengers in the minivan, a 58-year-old man and 13-year-old boy were injured and transported to Harborview Medical Center. The driver of the pickup, a 44-year-old Tukwila woman was injured and transported to Harborview. State Patrol has not determined if drugs or alcohol were factors in the crash, and charges are pending.