railroad car vs railway car

railroad car and railway car both are nouns.

Word	Noun	Adjective	Verb	Adverb
railroad car	Yes	No	No	No
railway car	Yes	No	No	No

As nouns, railroad car and railway car are synonyms defined as:

railroad car and railway car: a wheeled vehicle adapted to the rails of railroad

Other synonyms of railroad car include car, railcar.

railroad car (noun)	railway car (noun)
a wheeled vehicle adapted to the rails of railroad	a wheeled vehicle adapted to the rails of railroad