The ways they all died at each stop...
..to me clearly resembles how they died in the crash:
*The son, as his mother later says in the car, was "burned alive" (remember his charred arm as she hugged his body on the road?) so I guess that was his gruesome fate in the crash.
*The father clearly gets beheaded when he was pursuing the lady into the forest at the end (machete-like sound effect, sudden cut-off of his voice, thumping sound of a heavy object on the forest ground) so he presumably lost his head in the crash.
*The mother gets out of the car at 70 mph so she probably is also catapulted out of the vehicle onto the street in the real crash.
*Her fiancé has been reduced to a bloody pulp on the street when they pull out his cellphone (was that his ear dangling from it?) so he probably was thrown out of the car as well and wrapped himself around a tree.
Any thoughts...?