The SPMT's shown here are Goldhofer's. There are several manufacturers making this type of unit including Scheuerle, Kamag, Cometto, Nicolas, and Anster and they all essentially the same in their construction and operation. For highway use they will frequently remove the power unit and pull them with a tractor unit. If the terrain is more demanding, they can be rigged up with a pusher pull setup using two tractors fore and aft. There are also SPT trailers that do not use hydraulics but linkages to control the unit.