Why is a subway underground?

Answer 1

If they were not underground they would be called a railway. they are put underground because the railways that run on the surface use up large tracts of valuable land. by putting them underground the land can be used for buildings.

Answer 2

The prefix sub- means below, so the subway is a way to get around underground.

Answer 3

Because it is less money though more clasterfobic..... good question