What is the expiation for a car rollover accident that led to the death of an elderly widowed woman, knowing that the accident occurred due to shifting sands that caused the car to lose control?

If the driver was not negligent by exceeding the speed limit or failing to slow down in a dangerous area, and was unable to prevent the accident, then there is no blood money (diyyah) on his 'aqilah (male relatives responsible for paying blood money) and no expiation (kaffarah) on him. However, if he was negligent, then expiation is binding upon him, and blood money is binding upon his 'aqilah.