Truck-tractor semitrailer-semitrailer.
Truck-tractor semitrailer-semitrailer. In a truck-tractor semitrailer-semitrailer combination vehicle, the two trailing units are connected with a B-train assembly. The B-train assembly is a rigid frame extension attached to the rear frame of a first semitrailer which allows for a fifth wheel connection point for the second semitrailer. This combination has one less articulation point than the conventional A dolly connected truck-tractor semitrailer-trailer combination.