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 heavy tractor unit and multi-axled lowboy flatbed trailer. Some trailers may have independently steerable wheels, and several might be towed by one or more tractor units in a train.
Self-propelled modular transporters, some featuring a dozen and more self-steering axles with scores of rubber tires to spread out a load, are increasingly being manufactured. The ability of combination and self-propelled heavy haulers to carry loads of 100 tons is not unusual.
In some cases a heavy hauler is designed and constructed to move a particular load on a one-off or short-term basis. An example is the self-propelled antenna transporter for the ALMA radio telescope project, a 130-tonne (130-long-ton; 140-short-ton) 28-wheeled rigid vehicle designed to carry and place 115-tonne (113-long-ton; 127-short-ton) radio telescope antennas up a mountain to an altitude of 5,000 m (16,400 ft). Girder bridge trailers are also another specialist heavy hauler, specifically for the transport of large power transformers.
Typical loads moved by heavy haulers under escort on highways include giant boilers and pressure vessels used in the chemical industries, industrial plants, prefabricated sections for construction projects, giant power transformers, turbines, and houses (generally made of timber).
The term "heavy hauler" may also be used to refer to off-road dump trucks and ore carriers used in mining and construction with capacities up to 400 tonnes (390 long tons; 440 short tons), or an airplane that has been especially constructed for moving heavy materials.
There are some shipbuilding companies using SPMT for carrying ship parts and constructing ships in China. They have reduced million dollars of cost that were consumed for transporting loads using gantry cranes. It is also the first companies which use SPMT to build ship in China.