A ballast tractor is a specially weighted tractor unit of a heavy hauler combination. It is designed to utilize a drawbar to pull or push heavy or exceptionally large trailer loads which are loaded in a . When feasible, lowboy-style semi-trailers are used to minimize a load's center of gravity. Typical drivetrains are 6×4 and 6×6 but also available in 8×6 and 8×8. Typical ballast tractor loads include oil rig modules, bridge sections, buildings, ship sections, and industrial machinery such as generators and turbines.