Is the expiation for breaking a fast (kaffarat al-siyam) obligatory for someone who hit a person with their car, and the person died two days later, knowing that the deceased was crossing the road quickly and the road is known for its high speed and is not for pedestrians?

If death is caused by an accident, then the killing is an error on the part of the driver, and he is liable for diyah (blood money) and kaffarah (expiation). The diyah is borne by the 'Aqilah (male relatives on the father's side).

If the injured party had an effective role in causing the outcome, then the perpetrator is not liable if he was unable to avoid the accident.

If the driver could have avoided the accident but did not, then he is liable for compensation due to his negligence, and for kaffarah.

If he could not avoid it, then he is not liable for compensation nor for kaffarah.