bilevel railcar vs railway car

bilevel railcar and railway car both are nouns.

Word	Noun	Adjective	Verb	Adverb
bilevel railcar	Yes	No	No	No
railway car	Yes	No	No	No

As nouns, railway car is a hypernym of bilevel railcar; that is, railway car is a word with a broader meaning than bilevel railcar:

bilevel railcar: a type of rail car that has two levels of passenger accommodation, as opposed to one, increasing passenger capacity.
railway car: a wheeled vehicle adapted to the rails of railroad

Other hypernyms of bilevel railcar include car, railcar, railroad car.

bilevel railcar (noun)	railway car (noun)
a type of rail car that has two levels of passenger accommodation, as opposed to one, increasing passenger capacity.	a wheeled vehicle adapted to the rails of railroad