A fan made expansion designed by David Fair and available for download from the Geek.
The board: (full size PDF, needs to be cut for printing, 24x18" single page)
This map is designed for 4-6 players, and incorporates a number of rules variations, including a modification of Ted Alspach's chain delivery mechanic, and a creative new rule that allows players to place factories onto cities. The factories, in thematic fashion, mean that cities will gain more goods, as each time a delivery is made to the city, two more goods are placed onto it. Factories also give bonus income to their owner when a delivery is made to their locale, but they also increase end of round expenses.