Abstract: A steering system for steering a heavy haul trailer dolly comprising a turntable mounted on the dolly for connecting to another trailer unit. The dolly comprising a main frame, a wheel group mounted to the main frame, and a pivot frame mounted to the main frame between the turntable and the wheel group. A counter-steering linkage connects the pivot frame and the turntable. Hydraulic cylinders connect the pivot frame and the wheel group. To automatically steer the dolly, the hydraulic cylinders are locked in length. Rotation of the turntable in one direction causes the pivot frame and the wheel group to rotate in the opposite direction. To steer the dolly directly, the hydraulic cylinders are operated to extend and retract, pushing and pulling against the pivot frame and turntable to rotate the wheel group.

Abstract: An improved articulated heavy haul trailer combination comprises a trailing accessory vehicle such as a booster coupled to a main trailer by a coupling. The coupling includes a horizontal hinge, a vertical hinge that allows the trailing accessory vehicle to yaw in a horizontal plane, a spreader extending between the hinges and a hydraulic piston and cylinder. A turn sensor mounted on said combination detects yawing, and a controller reduces the piston and cylinder's downward biasing force on the coupling.