Pit and Underpass

Pit noun - A sunken area forming a separate space.

Underpass and pit are semantically related In some cases you can use "Underpass" instead a noun "Pit".

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

Pit and underpass are semantically related in covered passageway topic. Sometimes you can use "Pit" instead a noun "Underpass".