A SPMT combination consists of two units; a trailer unit and a power pack unit (PPU). The power pack unit powers the machine and is usually mounted at the rear. A trailer unit comprises 4, 5, 6 or 8 axle lines. The units can be joined together in a variety of configurations. Like a giant Meccano system, everything fits together. All wheels steer through 360 degrees, enabling the vehicle to drive forwards, backwards, sideways, diagonally, through a radius and even carrousel. All functions are operated and controlled by a single operator, working from one central panel, irrespective of the number of axle lines involved. The loading surface can be adjusted from 1200 to 1800 millimeters height, so that the load can be lifted and set down onto the supports without the use of auxiliary equipment. Moreover, the hydraulic suspension system compensates for tilted road surfaces, allowing the load to be kept level under all circumstances. It also allows the wheels to adjust themselves automatically to any bump in the road surface.