Railroad suburbs were primarily developed during the Victorian era, fin-de-siècle, and into the 1920s. Aping developers' success in using streetcar lines to sell new housing, several railroads decided to enter the development game themselves and build "New Towns" lineside. This pattern--small, semi-dispersed centers of population highly centralized around train stations (a major railroad suburb giveaway is when a train station lies at one end of Main Street) became a primary mode of outward urban expansion for the better part of a century, and has left us a rich heritage of the nicest, leafiest communities in cities all across the nation. And, despite catastrophic disinvestment in anything that wasn't a house farm from the 1950s to the early 2000s, railroad suburbs continued to be the effective archetype of quality American community.
New Urbanism got its start replicating railroad suburbs as new towns--even if the original railroad discontinued passenger service, the railroad suburb is, for all intents and purposes, a new town. Duany and Plater-Zyberk folded in some Southern Baroque town planning tradition, and--voilà!--an alternative to house farms, Levittown tracts, and meandering anti-grids was born.
There are profound implications to this. First, one of the great successes of the movement is the re-creation of the railroad suburb. Transit-Oriented Development, an idea about as old as New Urbanism, is (in essence) a manner of development built on the workings of a railroad suburb.
Italy is at the vanguard of the trend--we have reclaimed the development model associated with a smaller, smarter, more compact type of urbanism and town-building.