Wind energy components, industrial boilers, bridge girders or complete production plants – when standard vehicles are no longer enough, the world of abnormal loads begins. The choice of vehicle decides more than just the price: it determines whether the route can be permitted at all. A trailer that builds too high fails at the bridge clearance; too few axles fail on the permissible axle load. This guide classifies the most important vehicle types – and explains what Oversize Transports bases its equipment selection on for your project.
Semi low-loader: the workhorse up to medium weights
The semi low-loader (step-frame low-loader) has a lowered deck behind the gooseneck and is suitable for construction machinery, forklifts, compact machines and container-like cargo. Advantages: quick availability, easy loading via ramps, moderate cost. Typical payloads are in the range of up to around 50 t, depending on the number of axles. For tall cargo it is only suitable to a limited extent, because the deck sits higher than on a true low-bed.
Low-loaders and low-bed trailers: for tall and heavy loads
The low-bed trailer carries its deck between the axle groups only a few decimetres above the road surface. That creates valuable centimetres in overall height – often the difference between a direct route and weeks of detours. Telescopic variants adapt to different cargo lengths, and detachable goosenecks allow loading from the front. Depending on the axle configuration, low-bed combinations roughly cover the range from 50 to over 100 t. Typical loads: transformers, press components, machine beds, top-class excavators. Note the low ground clearance: ramps, level crossings and uneven site accesses must be checked in advance so that the combination does not ground out.
Modular trailers: when it goes beyond 100 t
For extreme loads, modular heavy-duty axle lines are used: hydraulically suspended platform lines that can be coupled in length and width and distribute the load across many axle lines. This keeps axle loads within the permittable range despite three-digit tonnages. In this class we move reactors, generators, transformers and plant modules up to 200 tonnes. SPMTs (self-propelled modular transporters) complete the spectrum on plant premises and for final positioning: remote-controlled, accurate to the millimetre, with every axle individually steerable and liftable – ideal for setting a module down exactly on its foundation.
Special solutions for excess length
Where length rather than weight is the issue, different rules apply:
- Telescopic trailers extend to the cargo length – for steel girders, masts and long machine components.
- Inloaders take long components between the vehicle structure and keep the overall height low.
- Dollies with steered axles carry the end of the cargo freely – the standard principle for rotor blades and bridge girders, because the cargo itself acts as a load-bearing element and tight bends become passable through forced steering.
- Boiler frames span long cylindrical components such as columns between two running gears.
What determines the right vehicle
The selection always follows the same criteria: weight and centre of gravity (determine axle count and load distribution), dimensions (determine deck height and trailer type), axle loads along the route (bridges set the hard limit) and the situation at the loading and unloading point (ramp, crane, manoeuvring area). That is why with us the feasibility study comes before the vehicle decision – not the other way round. A nominally cheaper vehicle quickly becomes expensive if it forces a longer permitted route or additional escort conditions.
Don't forget: the tractor unit
The right heavy haulage tractor unit is part of the vehicle concept too. From high gross combination weights upwards, machines with a reinforced drivetrain and ballast weights are necessary; on the heaviest combinations, a second tractor unit pushes or the combination runs in pull-push mode, for instance on gradients. This is permit-relevant as well: the authority assesses the entire vehicle combination including axle loads and engine power, not just the trailer. And finally, every combination needs the appropriate exemption permits under the German vehicle licensing regulations (StVZO) – the transport permit and the vehicle permit must match each other.
Advice from Oversize Transports
We analyse your cargo data, survey routes including bridge loads and headroom and select the most economical permittable equipment – from the semi low-loader to the modular heavy haulage combination for loads up to 200 tonnes. You receive a fixed-price quotation depending on route, weight and permit situation, including BF3/BF4 escorting and permit management. Send us dimensions, weight and lane – we will promptly recommend the right vehicle solution for you.
Vehicle types compared
| Vehicle type | Suitable for | Characteristic |
|---|---|---|
| Semi-trailer / flatbed | long or slightly oversize components, palletised heavy cargo | standard deck height, economical |
| Semi low-loader | construction machinery, transformers, tall pieces | lowered deck, reduced overall height |
| Low-loader / low-bed | heavy and tall machinery, boilers | very low deck height, high payload |
| Modular trailer / SPMT | heavy lift from 100–200 t and above | scalable axle by axle, partly self-propelled |