Heavy hauler in the context of MAN SE

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 hydraulic modular trailer. When feasible, lowboy-style semi-trailers are used to minimize the height of a load's center of mass. Typical drivetrains are 6×4 and 6×6, but 8×6 and 8×8 are also available. Typical ballast tractor loads include oil rig modules, bridge sections, buildings, ship sections, and industrial machinery such as generators and turbines.

Only a handful of manufacturers produce dedicated ballast tractors. Extra-heavy-duty chassis versions of mass-production tractor units are fitted with drawbar hitches and a separate ballast box as an alternative. These units are classified as N3 Category of large goods vehicle. Ballast tractors can be traced back to the 1940s when heavy haulers from the UK started employing purpose-built Scammell Showtracs, a short wheelbase 4×2 ballast tractor.

A hydraulic modular trailer (HMT) is a platform trailer unit that features swing axles, hydraulic suspension, independently steerable axles, two or more axle rows, compatibility to join two or more units longitudinally and laterally, and uses a power pack unit (PPU) to steer and adjust height. These trailer units are used to transport oversized loads, which are difficult to disassemble and are overweight. Trailers of this type are manufactured using high-tensile steel, which allows them to support heavy loads. They are operated by one or more ballast tractors that push or pull the trailer using a drawbar or gooseneck connection. This tractor-trailer arrangement is commonly referred to as a heavy hauler.

Typical loads include oil rig modules, bridge sections, buildings, ship sections, and industrial machinery such as generators and turbines. Also, militaries use HMT for tank transportation. There is a limited number of manufacturers who produce these heavy-duty trailers because the market share of oversized loads is very thin when we talk about the overall transportation industry. There are self-powered units of hydraulic modular trailers, which are called Self-propelled modular transporters (SPMTs), which are used when the ballast tractors are unable to be used due to space.