impasse vs blind alley

impasse and blind alley both are nouns.

Word	Noun	Adjective	Verb	Adverb
impasse	Yes	No	No	No
blind alley	Yes	No	No	No

As nouns, impasse and blind alley are synonyms defined as:

Other synonyms of impasse include cul de sac, dead-end street.

impasse (noun)	blind alley (noun)
a street with only one way in or out	(figurative) a course of action that is unproductive and offers no hope of improvement
a situation in which no progress can be made or no advancement is possible	a street with only one way in or out