What was the cause of Heloise's father's death in the short-story, The Other One?

Heloise's father and Barbie were killed in a car crash while traveling in France. Clifford traveled to France with Delia, his lover, and Barbie, her friend when he was supposed to be in Germany. During the accident, the car spun across two lanes of traffic and hit a tractor-trailer. Barbie died instantly, and Clifford was taken to the hospital, where he died a few days later.