A heavy hauler is a very large transporter for moving oversize loads too large for road travel without an escort and special permit.
A heavy hauler typically consists of a Ballast Tractor and a hydraulic modular trailer, or using a 6x4 tractor unit with a lift axle pulling a removable gooseneck trailer or double-drop trailer. Some trailers may have independently steerable wheels, and several might be towed by one or more tractor units in a train.
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.
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