Yes, CARS is a Scrabble word!

Letter values in Scrabble US: C 3, A 1, R 1, S 1.

Is it a valid word?

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

a motor vehicle with four wheels; usually propelled by an internal combustion engine
a wheeled vehicle adapted to the rails of railroad
the compartment that is suspended from an airship and that carries personnel and the cargo and the power plant
where passengers ride up and down
a conveyance for passengers or freight on a cable railway

Also: railway car, railroad car, elevator car, cable car.