The South Dakota Highway Patrol said today it has been unable to determine the cause of a February 23 crash on Interstate 90 that killed four members of a Sioux Falls family.
James Arthur Vollmer, 52, of Sioux Falls was driving a 2005 Ford Explorer Sport Trac that drifted off the interstate into the median and crashed shortly after 5 p.m.
Vollmers wife Julie, 48; daughter Allysa, 16, and son Caleb, 13 were also killed in the crash.
An autopsy found no evidence of a medical problem or condition that could have contributed to the crash, said capt. Kevin Joffer of the highway patrol's Sioux Falls district office.
A mechanic who examined the vehicle found no evidence of a mechanical failure or problem, Joffer said.
Toxicology reports showed no evidence of drug or alcohol use, and the investigation found no evidence of any adverse weather or roadway conditions, any animals or any other vehicle involvement that could have caused or contributed to the crash.
There was no evidence of texting or cell-phone use, and witness statements indicate that Vollmers vehicle was traveling at about the same speed as other vehicles on the interstate.
The crash happened one mile west of Sioux Falls at mile marker 394. All four occupants were wearing seatbelts.
"At this point, we are unable to say what caused this tragic crash,'' Joffer said. "We have conducted a thorough investigation. If additional leads are developed, we will investigate them just as thoroughly. We join with the rest of the community in expressing our sorrow at the loss of this family.''