scenic railway vs railroad line

scenic railway and railroad line both are nouns.

Word	Noun	Adjective	Verb	Adverb
scenic railway	Yes	No	No	No
railroad line	Yes	No	No	No

As nouns, railroad line is a hypernym of scenic railway; that is, railroad line is a word with a broader meaning than scenic railway:

scenic railway: small railway in an amusement park
railroad line: line that is the commercial organization responsible for operating a system of transportation for trains that pull passengers or freight

Other hypernyms of scenic railway include railroad, railway, railway line, railway system.

scenic railway (noun)	railroad line (noun)
small railway in an amusement park	line that is the commercial organization responsible for operating a system of transportation for trains that pull passengers or freight