When you're trying to move around, seated in a chair on wheels, it's easier to move while moving _*BACKWARD*_.
This makes me believe that the car of the #Flintstones was incredibly inefficient. Think about it, moving _forward_ in a seat-with-wheels is hard, while moving backward is easy.
For the Flintstones, it would therefore be a lot more efficient if they had a single driver facing #forward and breaking, and the passengers facing #backward and providing the power to move the #vehicle.