Yes, LOCOMOTIVE is a Scrabble word!

Letter values in Scrabble US: L 1, O 1, C 3, O 1, M 3, O 1, T 1, I 1, V 4, E 1.

Is it a valid word?

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

a wheeled vehicle consisting of a self-propelled engine that is used to draw trains along railway tracks

Also: locomotive engine, railway locomotive.