Rack railway and Railroad line

Rack railway noun - Railway for steep mountains; a cogwheel on the locomotive engages cogs on a center rail to provide traction.

Railroad line and rack railway are semantically related. In some cases you can use "Railroad line" instead a noun phrase "Rack railway".

Railroad line noun - Line that is the commercial organization responsible for operating a system of transportation for trains that pull passengers or freight.

Rack railway and railroad line are semantically related. Sometimes you can replace phrase "Rack railway" with "Railroad line", this phrases are similar.