superhighway vs state highway

superhighway and state highway both are nouns.

Word	Noun	Adjective	Verb	Adverb
superhighway	Yes	No	No	No
state highway	Yes	No	No	No

As nouns, superhighway and state highway are synonyms defined as:

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

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

superhighway (noun)	state highway (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