bilevel car vs railroad car

bilevel car and railroad car both are nouns.

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

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

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

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

bilevel car (noun)	railroad 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