B-double

So-called -"double" in Australia partly because of industry concerns about negative public attitudes to road trains. The "B" refers the load sharing axle group of the bridge "B" lead trailer with a 5th wheel coupling at the rear (between the trailers)- followed by a 5th wheel/turntable connected semitrailer as the second in the configuration. B-Doubles were initially developed in Canada, as B-Trains. The Australian freight road industry was able to persuade Governments to call them B-Doubles. This was to reduce potential confusion with road trains and also help overcome some public opposition that persisted, in some urban areas, to the mid-1990s. Note: the "A" in Road-Train nomenclature refers to the "A-Frame" drawbar inherent to many "dog-trailer"/dolly converter type of trailer (ie. when a semitrailer is converted into a Dog-trailer by the inclusion of a 2 or 3 axle "Dolly" Converter (containing a 5th wheel coupling), the assumption is that all trailer types are being hauled by a Semi-PrimeMover (Articulated Tractor unit) via a 5th wheel/turntable connection). Calling the "Lead-trailer" the "A", or calling a regular semi trailer in the train a "B" trailer - or vice versa, confuses the reason why the A and B are used and overlooks that both the A-converter and B-Trailer, are in reality types of dolly (both are also registered as individual trailers) which convert a semitrailer into a self steering unit (dog trailer) - following the lead. A "B"-trailer (bridge) carries a load supported between the leading 5th wheel/turntable (mounted on either; another trailer, a dolly converter or the hauling tractor/PrimeMover) and its wheelset, while sharing its (rear) wheelset with the semi-trailer following on the turntable connector, while the "A" dolly-converter generally carries no load on the drawbar and places no (significant) load (or roll forces) in the leading trailer (or tractor) unit.