pedestrian bridge vs overcrossing

pedestrian bridge and overcrossing both are nouns.

Word	Noun	Adjective	Verb	Adverb
pedestrian bridge	Yes	No	No	No
overcrossing	Yes	No	No	No

As nouns, pedestrian bridge and overcrossing are synonyms defined as:

Other synonyms of pedestrian bridge include footbridge.

pedestrian bridge (noun)	overcrossing (noun)
a bridge designed for pedestrians	a bridge designed for pedestrians