Editing Network effect (section)

===Rail gauge===
[[File:Rail gauge world.svg|thumb|350px|The dominant rail gauge in each country shown]]
There are strong network effects in the initial choice of [[rail gauge]], and in [[gauge conversion]] decisions. Even when placing isolated rails not connected to any other lines, track layers usually choose a standard rail gauge so they can use off-the-shelf rolling stock. Although a few manufacturers make rolling stock that can adjust to different rail gauges, most manufacturers make rolling stock that only works with one of the standard rail gauges. This even applies to [[urban rail]] systems where historically [[tram]]ways and to a lesser extent metros would come in a wide array of different gauges, nowadays virtually all new networks are built to a handful of gauges and overwhelmingly [[standard gauge]].