From what I understand the requirement for a Bachelor's degree is fairly new and may be a result of the tight job market.
The on-car supervisor is responsible for their group of drivers. They deal with everything from staffing, customer concerns, on road observations, annual safety rides, training new drivers and driver performace. The on-car position is not an easy one. The initial pay is generally less than that of a FT driver with the difference being made up in MIP. My on-car, who drove for 15 years and is retiring in less than two months, was able to use his MIP to help put his three children through college and walk one of his daughter's down the aisle. He would also be the first to tell any hourly thinking of making the jump not to do it.