There are rules for railroads in other games. If we were to extrapolate those rules we could easily set up rails for each nation.
1) Russia: Infantry, Artillery and AA Guns may move two territories along Buryatia, Yakut, Novosibirsk, Kazakh, Russia, Archangelsk, Karelia, W. Russia and Caucasus. No cost.
2) Germany: Infantry, Artillery and AA Guns may move two territories along Belorussia, Ukraine, Balkans, S. Europe, E. Europe, W. Europe and Germany, no cost.
3) England: Infantry, Artillery and AA Guns may move two territories along India, Persia, Trans-Jordan, Egypt, Italian Africa, Kenya, S. Africa, Congo, Fr. Equatorial Africa and Fr. West Africa
4) Japan: Infantry, Artillery and AA Guns may move two territories along Manchuria, Kwangtung and Fr. Indo China
5) USA: Infantry, Artillery and AA Guns may move two territories along Alaska, W. Canada*, W. USA, C. USA and E. USA
- Note: America is allowed through W. Canada on rail just to get to Alaska. Units would not be able to travel by rail from E. USA to W. Canada. The only way to use W. Canada in this manner would be to send units from C. USA or W. USA to Alaska or from Alaska to W. USA or C. USA.
There is no cost to using the rail and unlimited numbers of units can travel along it.