Here is the lowdown: Transit fares generally don't cover operating expenses. Transit systems do not, unfortunately, turn a profit. In many conservative circles, this is considered a damning indictment of the whole idea of public transit -- which is itself a damning indictment of the analytical powers of the guilty conservatives.
We should expect those who benefit from a technology to pay for it. This is the basic idea behind a market economy -- people aren't in the habit of giving away something for nothing, and the best way to allocate scarce resources is to let buyers and sellers agree upon a price, which is then paid by the buyer who, we expect, will benefit from the purchase.
But sometimes, when a buyer decides to spend money on a good or service, other people benefit as well. If I build an exceptionally attractive house in a neighborhood, I benefit, but so too do my neighbors, who get to look at the house and whose own homes may appreciate thanks to their location in what is now a more attractive neighborhood. When I pay college tuition and get a degree, I benefit, but so too do future colleagues, who will enjoy greater success as part of a highly educated labor pool. If government does nothing in such situations, then we will get the level of attractive homes or college educations that suits the direct beneficiaries of such investments -- but that doesn't mean that we have provided the number that maximizes the benefit to society as a whole.
