 Some rail lines experimented with multiple unit configurations, where streetcars were joined together to make short trains.When lines were built over longer distances (typically with a single track) before good roads were common, they were generally called "interurban streetcars" or "radial railways" in North America.After World War II, seven major North American cities (Boston, Newark, New Orleans, Philadelphia, Pittsburgh, San Francisco, and Toronto) continued to operate large streetcar systems.