What is the expiation for hitting and killing a person with a car, knowing that the speed was legal?

If an accident occurs due to a sudden appearance of a woman and it could not be avoided without error or transgression on the part of the driver, then there is no blame on him and no expiation, based on the jurisprudential rule: "What cannot be avoided entails no liability." However, if there was an error or negligence on the part of the driver, or he could have avoided the accident but did not, then he is liable for diyah (blood money) and expiation. The final ruling in these matters rests with the Sharia courts to investigate the circumstances of the accident.