Actually,

C. When a pilot is required to train away from his Base and has a scheduled duty free period of forty-eight (48) hours or more during such training, he will be provided on- line, positive space, round trip transportation (PS-5 or comparable class) between the training facility and his home or Base (at the pilot’s option) in order to accommodate his scheduled duty-free period.

This is right out of the contract. PS means positive space, not standby. PS0 is the only "must ride", I have never been bumped from a flight.