A motion regulation system to control relative motion between a vehicle and a boom structure mounted to the vehicle. The boom structure comprises two booms that are mounted on opposite sides of a central mount the two booms being rotatable relative to the central mount and to one another. The central mount is mounted to the vehicle to allow relative rotation between the vehicle and the central mount. The motion regulation system comprises two gas bags(air/hydraulic springs) connected to and arranged between the central mount and the vehicle and means to determine that the vehicle has or is about to roll relative to the boom structure or visa-versa, and in response to alter the pressure of gas within one or both of the gas bags. Preferably the system comprises means to sense and control the gas pressure within at least one gas bag. Preferably there are means to calculate average gas pressure and to adjust accordingly. Preferably there is a conduit between the gas bags to allow gas to flow between the bags to equalise pressure. Preferably there are means to detect a change in the relief of the ground in front of the vehicle.
