Dear Dr. Boli: I visited Pittsburgh recently, and I miserably failed in trying to figure out the transit system there. It was not the map, which was explicit enough; it was the question of when to pay my fare. Why is such a simple thing so convoluted? Since I know that Pittsburgh is the capital of your celebrated publishing empire, I thought you might be able to explain it to me. —Sincerely, a puzzled Chicagoan.

Dear Sir or Madam: It is not so terribly convoluted if you remember the simple rules that govern the payment of fares on all Port Authority transit. Inbound, you pay when you get on; outbound, you pay when you get off; unless the route does not go downtown or it is after 7 p.m., in which case you pay when you get on, unless it is a trolley route, in which case you still follow the daytime rules; or unless you are going from one part of downtown to another, in which case you do not pay at all, unless it is after 7 p.m., in which case you pay when you get on a bus, but the subway is still free; and the subway is also free north of the Allegheny, but the buses are not; but the subway is not free south of the Monongahela; and on the Duquesne Incline you pay at the bottom station, but on the Monongahela Incline you pay at the top. Just remember these simple rules, and you will never be confused by Pittsburgh transit again.