Self-Propelled Modular Transporters

A self-propelled modular transporter, usually called an SPMT, is a heavy transport platform made of modules with many computer-controlled axle lines. Each module has its own wheels, hydraulic suspension and steering, and several modules can be coupled side by side and end to end to form a single platform large enough to carry a bridge span, a refinery module, a ship section or even a whole building. The modules are driven by hydraulic motors supplied by a power pack unit, and the entire combination is controlled by one operator with a remote control.

SPMTs are not cranes, but they belong to the world of heavy lifting and heavy transport because they often work together with cranes, jacking systems and skidding systems. They move loads of hundreds or thousands of tonnes over short distances with great precision, and their ability to lift and lower the platform hydraulically lets them pick up a load from supports and set it down again without a crane.

Brief History of Self-Propelled Modular Transporters

Heavy multi-axle trailers with steerable wheels existed well before modern SPMTs. The modern concept developed in the 1970s and early 1980s, when heavy transport contractors needed a platform that could carry very heavy loads on site, steer in any direction and be configured for each job. The Dutch heavy transport company Mammoet and the German manufacturer Scheuerle worked together on the design, and deliveries of the first production SPMTs began in 1983. Among the principles established at that time was a standard module width of about 2.4 metres, which is still widely used and allows modules from different fleets to be combined.

In the following decades, electronic steering replaced mechanical systems, allowing modes such as crab, carousel and diagonal travel. Other manufacturers entered the market, module capacities increased, and SPMTs became essential tools for offshore fabrication yards, shipyards, power plants and bridge contractors. Accelerated bridge construction, in which a new bridge span is built beside the road and driven into place overnight, made SPMTs a familiar sight on infrastructure projects. Electric power pack units have been introduced in recent years.

How a Self-Propelled Modular Transporter Works

Modules and axle lines. Each module has several axle lines, commonly four or six, each with two pairs of wheels. Modules are joined mechanically and electronically to form a platform of the required size.
Power pack unit. A diesel or electric power pack supplies hydraulic oil to drive motors on some or all axle lines, and to the steering and suspension. Larger combinations use several power packs.
Hydraulic suspension. Every axle line has a hydraulic cylinder. The cylinders are connected in groups, usually three or four, which act as support points and share the load evenly even on uneven ground. The same cylinders raise and lower the platform, typically by several hundred millimetres.
Electronic steering. Each axle line can turn through a wide angle. The control system coordinates all axles so the combination can drive straight, turn about a centre point, move sideways or rotate on the spot.
Control. The operator walks alongside the transporter with a remote control, supported by spotters. Monitoring systems show pressures, heights and steering angles.
Speed. Fully loaded SPMTs move slowly, at walking pace or less, which allows precise positioning.

Types of Self-Propelled Modular Transporters

Standard SPMT Modules

Four-axle and six-axle modules with a width of about 2.4 m, used for most heavy transport work. They can be combined in almost any length and number of parallel lines.

Wide or Heavy-Duty Modules

Modules built for higher axle loads or greater stability, used for the heaviest loads and when a wider track is needed.

Compact and Light SPMTs

Smaller modular transporters for loads that are too heavy for trailers but do not require a full-size fleet, such as transformers or machinery in factories.

Self-Propelled Trailers and Combinations

SPMT technology is also used as self-propelled units within road-going heavy trailer combinations, or combined with conventional modular trailers.

Electric SPMTs

Modules powered by electric power pack units, which reduce noise and local emissions on urban and indoor projects.

Size and Capacity

Configuration	Typical payload	Typical use
Single module (4 or 6 axle lines)	about 100 to 250 t	Machinery, transformers, small structures
Medium combination (10 to 30 axle lines)	about 300 to 1,000 t	Bridge spans, process modules
Large combination (50 or more axle lines)	several thousand tonnes	Offshore modules, ship sections, buildings

Figures are indicative and depend on axle load, speed and ground conditions.

Accessories

SPMTs are used with spacers, turntables and bolsters that support the load above the platform, stools and cribbing on which the load is set down, and jacking towers or tower systems when the load must be raised higher than the suspension stroke. Stability monitoring systems, load cells and ground pressure calculations are part of most large moves. SPMTs can also carry cranes or be combined with skidding systems and ballast for load-out onto barges and ships.

Main Manufacturers

Scheuerle and Kamag, both part of the TII Group, which also includes Nicolas.
Goldhofer, a German manufacturer of heavy trailers and SPMTs.
Cometto, an Italian manufacturer of heavy transport equipment.

Large SPMT fleets are operated by heavy transport and lifting contractors such as Mammoet and Sarens.

Main Uses of Self-Propelled Modular Transporters

Moving and installing bridge spans, including accelerated bridge construction.
Loading out offshore modules, jackets and topsides onto barges.
Moving ship blocks and sections in shipyards.
Transporting refinery, petrochemical and power plant modules.
Relocating buildings and large structures.
Moving spacecraft, rockets and large scientific equipment.
Moving transformers, generators and heavy machinery on site.

Planning an SPMT Move

Engineering. Every heavy move needs calculations of axle loads, stability, ground bearing pressure and the load’s own strength.
Configuration. The number of axle lines, their layout and the suspension grouping are chosen to spread the load and keep the combination stable.
Route. Ground conditions, slopes, underground services, clearances and turning space are checked. Steel plates or mats may be needed.
Load interface. Supports, spreader beams and sea fastenings must match the load’s lifting and support points.
Timing. Bridge and road moves are often scheduled during short road closures, so rehearsals and contingency plans are common.
Clearances and height. The platform height, the stroke of the suspension and any stools or towers determine whether the transporter can drive under the load, lift it off its supports and set it down at the destination.
Team and communication. A move needs an operator, spotters at each corner, a supervisor and often an engineer on site. Radio communication and agreed stop signals are set before the move starts.
Weather. Wind limits apply to tall loads, and heavy rain can soften the ground along the route.

SPMT or Conventional Trailer?

SPMTs and conventional hydraulic modular trailers share many principles, but they suit different jobs. A trailer pulled or pushed by a heavy tractor is designed for longer journeys on public roads at higher speeds. An SPMT has its own drive on the axles, steers in almost any direction and moves very precisely, which makes it better for heavy loads over short distances, inside plants, on quays and in tight spaces. Some contractors combine both, using trailers for the road journey and SPMTs for the final positioning.

Safety

The main risks in SPMT operations are loss of stability, especially with tall loads, on slopes or when the suspension groups are not correctly configured, overloading of axles or ground, and people crushed or struck around a moving load. Industry guidance, including best practice documents issued by the European heavy transport association ESTA, emphasises stability calculations, trained operators and supervisors, clear communication and exclusion zones. The load must be secured to the platform, wind limits must be observed for high loads, and the route must be inspected before the move.

Trends and Technology

Electric power packs, remote monitoring and more advanced control software are the main developments. Digital planning tools simulate moves and stability in advance. Fleets continue to grow as offshore wind, bridge replacement and modular construction create demand for moving large prefabricated elements. Integration with jacking and skidding systems allows complete lifting and transport solutions from a single contractor.

Key Terms

Axle line: a pair of wheel sets across the width of a module, the basic unit of SPMT capacity.
Power pack unit (PPU): the engine or electric unit that supplies hydraulic power to the modules.
Suspension grouping: the hydraulic connection of axles into three or four support points.
Carousel steering: a steering mode in which the transporter rotates around a centre point.
Load-out: moving a heavy structure from quay to barge or ship.
Accelerated bridge construction: building a bridge span off site and moving it into position quickly.

Frequently Asked Questions

What does SPMT stand for? Self-propelled modular transporter, a heavy transport platform built from modules with computer-controlled axles.

How much can an SPMT carry? A single module carries tens to a few hundred tonnes. Combined modules have moved loads of many thousands of tonnes.

How fast does an SPMT move? Loaded SPMTs typically move at walking pace or slower, since precise control matters more than speed.

Can SPMTs drive on public roads? Usually only under special permits during planned closures. For long road journeys, conventional modular trailers are used.