railroad train vs roll-on roll-off

railroad train and roll-on roll-off both are nouns.

Word	Noun	Adjective	Verb	Adverb
railroad train	Yes	No	No	No
roll-on roll-off	Yes	No	No	No

railroad train (noun)	roll-on roll-off (noun)
public transport provided by a line of railway cars coupled together and drawn by a locomotive	a method of transport (as a ferry or train or plane) that vehicles roll onto at the beginning and roll off of at the destination