What is the ruling of Islamic law regarding obligating a driver who is driving his car properly to pay the blood money (diyya) for three people who died as a result of being hit by a swerving car, even though the fault has been established by traffic police as resting with the other car? And is he also obligated to fast?

If the driver adhered to safety measures and traffic laws, and an accident occurred, then there is no blood money (diyya), no expiation (kaffara), and no sin upon him. However, if he was negligent or violated traffic laws and was the cause of the accident, then blood money is upon him along with his 'aqila (male relatives on the father's side), and expiation is upon him. The specialized authorities (traffic police and courts) determine who is responsible for the error.