railroad engineer vs locomotive engineer

railroad engineer and locomotive engineer both are nouns.

Word	Noun	Adjective	Verb	Adverb
railroad engineer	Yes	No	No	No
locomotive engineer	Yes	No	No	No

As nouns, railroad engineer and locomotive engineer are synonyms defined as:

railroad engineer and locomotive engineer: the operator of a railway locomotive

Other synonyms of railroad engineer include engine driver, engineer.

railroad engineer (noun)	locomotive engineer (noun)
the operator of a railway locomotive	the operator of a railway locomotive