Is expiation (kaffarah) or blood money (diyah) obligatory in a car accident that led to the death of a Coptic individual, knowing that the accident occurred within the legal speed limit and a court ruling acquitted the driver?

If you were not negligent or careless, and you had taken all safety precautions, and it was not possible to avoid the accident, then there is no blood money (diyya) upon you, nor expiation (kaffara), nor sin; because what cannot be avoided does not incur liability. Liability arises from direct action or from causation if the cause was a transgression. There is no difference in this regard between a Muslim and a non-Muslim.