21. Where an axle group of a vehicle has attached to it a device that enables
the suspension of 1 or more of the axles of the axle group to be isolated from
the suspension of the other axle or axles of the axle group so that load
sharing among the axles of the axle group is altered or ceases, the controls
of that device shall be so located that they are not capable of being operated
by a person who is riding in or on the vehicle.