PIERRE, (KCCR) — A 38 year-old man was killed Sunday in a one-vehicle crash in Buffalo County. According to information released by the South Dakota Highway Patrol the crash happened Sunday morning just after three-A-M three miles east of Fort Thompson on South Dakota Highway 34. The preliminary investigation of the crash indicates the driver and a passenger were traveling west on Highway 34 when the 2008 Mercury Mariner S-U-V they were in left the highway. The vehicle crossed the eastbound lane then vaulted over a driveway approach and crashed in the south ditch. The 38 year-old driver was pronounced dead at the scene. The 23 year-old male passenger suffered life-threatening injuries in the crash. Neither were using seat belts at the time of the crash. The names of those involved in the crash are being withheld pending notification of family.