Originally posted by tim60 In Australia they have something that looks like it but is fundamentally different - B-double, standard short tractor + short trail + full length trailer, with each trailer supported by the rear axle of the thing in front.
Today, in North America there are A trains (doubles), B trains (doubles) and triples.
The A doubles have a long trailer (48 or 55 foot) connected by a 5th wheel plate to the tractor, and a short trailer (28 foot) the front of which rides on either a single or tandem set of axles that couples to the front trailer via a long tongue and a pintle hook.
B doubles have a long trailer (48 or 55 foot) connected to a 5th wheel plate on the tractor, and a short (28 foot) trailer that couples to the front trailer via a 5th wheel plate.
Trucks pulling triples are all 28 foot trailers. The front trailer connects to the tractor via a 5th wheel plate, the other two trailers connect via a converter dolly, which uses a pintle hook to connect at the front and has a single axle with a 5th wheel plate over it to connect and support the trailer.