Republicans have no problem driving on highways funded by the public or for that matter a multitude of public projects.
The difference is that Republicans have already been forced to pay for those things. They might as well use them. This is a cause of sprawl, btw.
Universities, on the other hand, collect tax dollars and their employees are paid with these dollars. Sure, there is nothing wrong with Republicans attending a university they'll be forced to subsidize later. But that's not the same thing.