coupling at both ends. Only some kinds of couplings coexist on the end of a wagon at the same time, because amongst other reasons they need to be at the same height. For example, in the Australian state of Victoria, engines had the AAR coupler, with buffers, and the chain mounted on a lug cast into the AAR coupler. A barrier vehicle / wagon in Britain and "transition car" in North America) has different kinds of couplings at each end. If a pair of barrier vehicles is used, a rake of wagons using coupling A can be inserted into a train otherwise using coupling B. A coupling adaptor or compromise coupler might couple to an AAR coupling on a wagon, and present, for example, a meatchopper coupler or rapid transit coupler to the next wagon. Such an adaptor might weigh . An adapter piece allows a Janney coupler mate with an SA3 coupler Dual coupling Sets of carriages Automatic couplers like the Janney are safer in a collision because they help prevent the carriages telescoping. British Rail therefore decided to adopt a Janney variant for its passenger carriages, with the coupler able to swing out of the way for coupling to engines with the traditional buffer and chain system. In New South Wales, sets of carriages were permanently coupled with a fixed bar, since the carriages were disconnected only at the workshops. Freight cars are sometimes coupled in pairs or triplets, using bar couplings in between. Articulated sets of carriages or wagons share the intermediate bogies, and have no need for couplings in the intermediate positions. Brake couplings Couplings are needed for any continuous braking systems. Electronically controlled brakes Electronically controlled pneumatic brakes (ECP) need a method of connecting electrically adjacent wagons, both for power and for command signals, and this can be done by plugs and sockets, or by very short range radio signals. Draw gear A draw gear (also known as a draft gear) is the assembly behind the coupling at each end of the wagon to take care of the compression and tension forces between the wagons of trains. Early draw gears were made of wood, which was gradually replaced by steel. Janney couplers have the draft gear in a centersill to absorb the pushing and pulling forces (slack action). There is also a draw gear behind tightlock couplers, SA3 couplers, C-AKv couplers, Scharfenberg couplers, and other