underpass

n.

An underground tunnel or passage enabling pedestrians to cross a road or railway.

subway

n.

In British English, subway normally refers to a specially constructed underpass for pedestrians and/or cyclists beneath a road or railway, allowing them to reach the other side in safety.

This term was also used in the past in the United States, but is now used to refer to underground rapid transit systems.

skyway

n. American English

A pedestrian overpass between two buildings.

It is usually owned by businesses and enclosed or covered to protect pedestrians from the weather.

Synonyms:

catwalk, skywalk, footbridge or pedway.