A moveable vehicle-trailer combination (11, 12) includes (a) a self-powered vehicle (11) having one or more surface-engaging members (13, 14, 16, 17) and a steering mechanism for steering at least one said surface-engaging member (13, 14) so as to cause changes in a direction of movement of the vehicle (11)； and (b) a trailer (12) that is towed behind the vehicle (11) as the vehicle (11) moves forwardly and is pivotably connected to the vehicle (11). The combination (11, 12) includes one or more forwardly effective sensors (27) for sensing one or more objects and/or artefacts and/or conditions located forwardly of the vehicle (11)； (d) one or more laterally effective sensor (29) for sensing one or more objects and/or artefacts and/or conditions that when sensed are located laterally of the vehicle (11) and/or the trailer (12)； and (e) a control and/or processing apparatus that acts in dependence on at least one output of the one or more laterally effective sensors (29) to take account of the presence of one or more objects and/or artefacts and/or conditions sensed by the one or more laterally effective sensor (29).
