A heavy hauler is a very large transporter for moving oversize loads too large for road travel without an escort and special permit.
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A heavy hauler typically consists of a Ballast Tractor and a hydraulic modular 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 (SPMT), some featuring a dozen or more self-steering axles with scores of rubber tires to spread out a load, are increasingly being manufactured. Working in coordinated teams, heavy haulers are able to carry loads exceeding 100 tons.