Train system (5)
(Other definitions for metro that I've seen before include "Paris subway" , "Paris underground rail system" , "The underground railway system in Paris" , "French underground" , "The Paris Underground transport system" .)
(Other definitions for railroad that I've seen before include "Push through unduly" , "Rush (someone) into doing something" , "Bully" , "[DRAGOON]" , "Coerce (someone) into doing something" .)