There may be a couple things at work here. For one, I think pmp6nl is right that NDSU is using student fees to pay for students/faculty/staff to use the bus system. For two, part of the benefit of encouraging students to use the bus system is that after they graduate they will be more likely to use public transportation and will pay back into the system at that point (by both paying for a service they have found to be useful and dependable and by choosing not to drive, which reduces traffic congestion on the metro area). If NDSU didn't make the bus system usable by students, those with cars would drive, increasing congestion and keeping them from understanding the benefits of public transportation, and those without cars would have to either not travel, find rides, or pay extra to ride the bus, all of which would encourage the creation of a class difference at NDSU, something that schools are generally trying to avoid.