He is a bus driver responsible for the safety of everyone on that bus. He isn’t sitting on his back porch squabbling with his wife!
Bus was parked during initial slap. Proper response:
1) Call station. Request immediate police presence.
2) Get out of seat. Inform woman under authority of the city, she is being detained for police.
3) If she attempts to leave, detain her, with progressively increasing force as needed.
4) Have her arrested when police arrive.
5) Pursue case vigorously in court on a personal level, and as a representative of the city.