A safety system for a riding lawn mower that prevents powered operation of a PTO driven implement while in reverse unless an override switch is "ON". The override switch may be a sustained action two position switch and the PTO driven implement may be a lawn mower blade. In one embodiment, the override switch does not allow the engine to start if the override switch is on. In one embodiment, the override switch cooperates with an operator presence switch to prevent operation of the PTO driven implement when the override switch is on and the operator is not present.