Wörterbuch Eisenbahn

[i] Underbridge (UK) ist „a bridge carrying the railway and allowing a roadway (etc.) to pass under the railway“. (http://en.wikipedia.org/wiki/Underbridge#U).
Eine Bahnüberführung, Eisenbahnbrücke, Wiadukt oder railway flyover wird in englischer Perspektive underbridge genannt, weil die obenliegende Eisenbahn „unterbrückt“ wird (Die Brücke wird unter der Eisenbahn gebaut). Eine overbridge ist dann einfach eine „bridge over a railway“. Also zum Beispiel eine Wegbrücke.

[ii] http://en.wikipedia.org/wiki/Feldbahn

[iii] Kleinbahn, Nebenbahn, Sekundärbahn, Feldeisenbahn, Feldbahn
Light rail is similar to the British English term light railway, long used to distinguish railway operations carried out under a less rigorous set of regulation using lighter equipment at lower speeds from mainline railways. Light rail is a generic international English phrase for these types of rail systems which means more or less the same thing throughout the Anglosphere.
Quelle: http://en.wikipedia.org/wiki/Light_rail,  und: http://fredriks.de/ed/ED3.htm#K

[iv] http://en.wikipedia.org/wiki/Kleinbahn

[v] As the main line network consolidated, railways were driven into the hinterland, serving local needs and commuter traffic. This was the age of the branch line or Nebenbahn (plural: -en), also variously called the Sekundärbahn („secondary line“), Vizinalbahn („neighbourhood line“) or Lokalbahn („local line“) depending on local laws and usage.