All praise is due to Allah, peace and blessings be upon the Messenger of Allah and upon all his family and companions.
If the traffic report has proved that the young man was to blame, then it is accidental killing, and so the person responsible must pay the Diyah. Allah, The Almighty, Said (What means): “Never should a believer kill a believer; but (If it so happens) by mistake, (Compensation is due): If one (so) kills a believer, it is ordained that he should free a believing slave, and pay compensation to the deceased’s family, unless they remit it freely. If the deceased belonged to a people at war with you, and he was a believer, the freeing of a believing slave (Is enough). If he belonged to a people with whom ye have treaty of Mutual alliance, compensation should be paid to his family, and a believing slave be freed. For those who find this beyond their means, (is prescribed) a fast for two months running: by way of repentance to God: for God hath all knowledge and all wisdom.” {Al-Nisa`/92}.
Accordingly, the Aqilah (male relatives of the killer`s clan from his father`s side)of the young man must pay the Diyah to the heirs of those killed in the accident. And Allah knows best.