Four people and a couple of things to pin on each of them. The passenger reads the setup, then the clues one at a time; you hold the grid in your head and say the answer when you have it. The clue set is minimal -- drop any one of them and there are two possible answers -- so par is hearing each clue once. Asking for a re-read is the only thing that costs, and that is the whole game.

Players: Two or more people in the car.

Driver: Solves it in their head. Asking for a clue again is what costs.

The bar: One reading per clue. Every clue matters, so there are no spare ones.