S04E12 Marge vs. the Monorail
After receiving a considerable donation of money, the people of Springfield decide what to spend it on. Enter Lyle Langley, a jocular salesman who gets Springfield hooked on a monorail system. After the monorail is up and running, and with Homer as the conductor, it's time for the maiden voyage. Little do the people know they have just boarded a one-way train to Hell.