Complex sentence: Grace and Jim try to warn the family of Ryder, but they are run off of the road by an oncoming tractor-trailer, Jim's car is totaled, forcing the couple to continue on foot.
Split into simpler sentences: Grace and Jim try to warn the family of Ryder, but they are run off the road by an oncoming tractor-trailer which totals Jim's car. With no other choice after Jim's car is totaled, the couple is forced to continue on foot.