A fan made expansion, like Japan, available from the base Age of Steam page. A bit more bare-bones in its presentation, but also fairly expansive, and helps fill the high scale niche.
The only special rule involves building a tunnel between two cities, which requires not only a large cash expenditure (8$), but the engineer role as well.
The files are available here:
http://www.boardgamegeek.com/fileinfo.php?fileid=7196