There is no Atonement Incumbent Upon Him
Question :
My father was involved in a collision with another car while he was driving. The driver of the other car died (may Allah have mercy on him). The Traffic Police determined that the fault was entirely that of the deceased and the family of the dead man waived (the right to the payment of) the Diyah may Allah reward them with goodness. Now I am asking: Is it incumbent upon my father to atone by fasting two consecutive months or not?
Answer:
If the matter is as you have described, then there is no atonement incumbent upon your father. That is because the fault was that of another, therefore he is not called a killer. And Allah is the Granter of success.
Source:
Ibn Baz
Fatawa Islamiyah, Vol. 6 Page 171