Yes, SUBWAYS is a Scrabble word!

Letter values in Scrabble US: S 1, U 1, B 3, W 4, A 1, Y 4, S 1.

Is it a valid word?

SUBWAYS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

an electric railway operating below the surface of the ground (usually in a city)
an underground tunnel or passage enabling pedestrians to cross a road or railway

Also: subway system.