There is a 13 page post regarding legality of weapons on a bus while traveling cross country. A solution might be Wasp Spray.
A lady who worked at a church in rough neighborhood called police to see if it was OK to keep mace handy as the counted Sunday's collection on Monday. The police recommended Wasp Spray because to use mace the offender has to be quite close but with Wasp Spray it shoots a spray 20 feet blinding the offender till they get to the Emergency Room for treatment. Simple solution and if your brother-in-law shows up drunk at your bus and knocks on the door, he would be less "dead".
It also works good on Wasp.