superhighway vs expressway

superhighway and expressway both are nouns.

Word	Noun	Adjective	Verb	Adverb
superhighway	Yes	No	No	No
expressway	Yes	No	No	No

As nouns, superhighway and expressway are synonyms defined as:

superhighway and expressway: a broad highway designed for high-speed traffic

Other synonyms of superhighway include freeway, motorway, pike, state highway, throughway, thruway.

superhighway (noun)	expressway (noun)
a broad highway designed for high-speed traffic	a broad highway designed for high-speed traffic
an extensive electronic network (such as the internet) used for the rapid transfer of sound and video and graphics in digital form