A system where a trailer/dolly (10) is lifted from the ground (by means of block and tackle, hydraulic rams, etc.) so as to locate beneath, or nest within, the chassis or sub-frame (12) of a vehicle. When it is to be used the trailer/dolly is either 'coupled under a vehicle or trailer as a dolly only' or it is lowered and moved rearwardly of the vehicle so it can be towed behind the vehicle using hitch (40). The chassis (14) of the trailer/dolly is in the form of a rectangular frame which can be enlarged in size by telescopic movements of members (20A, B; 22A, B etc.). A large number of small wheels (16A, B; 18A, B etc.) may be provided on sprung stub-axles.