SIOUX FALLS, S.D. (KELO AM) - The Highway Patrol is interviewing at least one witness to Saturday's fatal crash on I-90 that claimed the lives of four members of a Sioux Falls family.

Captain Kevin Joffer says the vehicle left the road, hit a guard rail cable, spun, vaulted off an embankment and crash-landed in a gully. Joffer says investigators are reconstructing the crash without the benefit of survivors. He says they're looking into medical conditions, mechanical factors; but it doesn't appear that road conditions were an issue.     

James and Julie Vollmer, and their two children, 16-year-old Alyssa and 13-year-old Caleb, died in the single vehicle crash. Joffer says the accident was hard on his troopers and a debriefing will be held soon with other emergency responders in an effort to help them cope with the tragedy. A surviving Vollmer sibling, Brittany, attends Northwestern College in Orange City, Iowa.