In bookstores in Rome, you can buy a poster headed, in English, i have a dream. It has nothing to do with Martin Luther King Jr. or the civil-rights struggle, instead being a map of an imaginary subway system that seamlessly connects all the neighborhoods of the city. In reality, Rome’s public-transportation infrastructure is shaky. Buses come infrequently. Many people resort to rented bikes or scooters. There is a subway system, with just three lines, connecting the central station to a few major places, but since it opened in 1955, it has grown at a sluggish…