Abstract: The invention provides a self-steering dolly that is rigidly releasably connected to the rear of a forward vehicle, such as a tractor-trailer combination, and supports the front end of a towed rearward vehicle, such as a second or "pup" trailer so that the vehicles are in tandem. The wheels of the dolly are mounted on respective king pins; are connected by a linkage and are urged to the neutral or straight-ahead position by a centering device. The means for releasably connecting the dolly and the forward vehicle comprise two transversely extending headed pins on the dolly of the kind employed with a fifth wheel connection engageable in respective releasable spring latches on the frame of the forward vehicle.