When I was in Paris they had teams of ticket gestapo, ahem, police, who would go to each passenger and ask to see their ticket. And if you don't have your ticket, they would issue a fine and pull out a card payment device. Honestly, I could not see SEPTA or the city going to such efficient lengths to deter the riff raff. But ANY kind of effort of enforcement would be better than what we have to put up with currently.