More often than not, an automobile - when parked or braked up a slope - will tend to roll backwards when started up a slope. It takes practice and skill on the part of the driver to control this backward roll to a minimum, to avoid colliding with automobiles on the rear side. Yet in a moment of lack of attention, an undesirable situation can occur.
To avoid this, a ratchet can be incorporated in the shafting mechanism - to prevent a roll backwards, while the vehicle is attempting to move forwards from the stopped position. The ratchet will have to automatically disengage when a reverse motion is attempted.