What is a Semi-Trailer Truck?
Understand semi-trailer trucks, their components, dimensions, trailer types, weight limits, and role in efficient European freight transport operations.
A semi-trailer truck is a road freight vehicle comprising two separable units — a tractor unit and a semi-trailer — connected by a fifth-wheel coupling. The tractor unit provides the engine, cab, and drive axles. The semi-trailer carries the cargo and has no front axle of its own. Under EU Directive 96/53/EC, the combination may not exceed 16.5 metres in total length or 40 tonnes gross vehicle weight across EU member states.
What are the main components of a semi-trailer truck?
A semi-trailer truck consists of two separable units — the tractor unit and the semi-trailer — joined by a fifth-wheel coupling on the rear of the tractor chassis. Both units fall under the truck and trailer types cluster in the Go Trans logistics glossary, which covers the full range of road freight vehicles used across European linehaul and distribution operations.
The tractor unit is the powered front section. It houses the engine, driver's cab, transmission, and drive axles — but carries no cargo of its own. European linehaul tractors run 400–500 hp diesel engines with 11–13 litre displacement and sit the cab directly above the engine. This cab-over-engine (flat-front) configuration is standard across European road freight and allows the maximum trailer length within the legal total vehicle length.
The semi-trailer is the rear unit that carries the load. Its defining mechanical characteristic is the absence of a front axle — the front of the trailer does not rest on its own wheels but on the tractor's fifth-wheel plate. Three rear axles carrying six sets of dual wheels support the trailer at the back. When the trailer is uncoupled from a tractor, retractable landing gear — steel support legs built into the trailer's front undercarriage — extend to hold the front off the ground.
The fifth-wheel coupling connects both units. A large horseshoe-shaped steel plate sits on the tractor's rear chassis. The trailer's kingpin — a vertical steel cylinder projecting from the trailer's front underside — locks into that plate at coupling. The plate holds the kingpin securely while allowing the trailer to pivot horizontally, which is what makes a 16.5 metre combination manoeuvrable in tight loading yards.
What is the difference between a semi-trailer truck and a rigid truck?
A semi-trailer truck separates the power unit from the cargo unit — a rigid truck integrates both on a single chassis that cannot be detached.
A rigid truck engine and load area share one permanent frame. The driver cannot disconnect the cargo section. The semi-trailer truck inverts that logic: the tractor drops a loaded trailer at a warehouse or terminal and collects another one immediately — it does not wait through the loading or unloading cycle. A rigid truck carrying a swap body container gains a similar drop-and-collect capability. The semi-trailer itself — the unpowered cargo-carrying unit — is covered in a separate glossary entry, including landing gear dimensions, axle configurations, and the range of trailer body types used across European freight operations.
A full trailer is not the same as a semi-trailer, though the two are often confused. A full trailer has its own front axle and can stand on its own wheels without any connection to a power unit. Full trailers are towed by rigid trucks using a drawbar coupling. A semi-trailer cannot stand unsupported at the front — it needs either the tractor's fifth-wheel plate or its own landing gear. That dependency is the reason the term "semi" appears in the name at all.
What are the EU dimensions and weight limits for a semi-trailer truck?
EU Directive 96/53/EC sets the maximum dimensions for semi-trailer trucks operating across EU member states — 16.5 metres total length, 2.55 metres width, and 40 tonnes gross vehicle weight.
The 16.5 metre total length covers the complete combination — tractor and semi-trailer together. European cab-over-engine tractors are shorter than North American bonneted trucks, which gives the trailer more of the 16.5 metres and increases load capacity within the legal limit. Width increases to 2.60 metres for refrigerated trailers to account for insulated wall thickness. For intermodal or combined road-rail transport, the GVW ceiling rises to 44 tonnes.
After deducting tractor tare weight (8–10 tonnes) and trailer tare weight (6–8 tonnes), the net cargo payload of a standard loaded semi-trailer truck runs to approximately 24,000–25,000 kg.
| Dimension / Weight | Standard Limit | Notes |
|---|---|---|
| Total length | 16.5 m | Tractor + semi-trailer combined |
| Width | 2.55 m | 2.60 m for refrigerated trailers |
| GVW | 40 tonnes | 44 tonnes for intermodal/combined transport |
| Net payload | ~24,000–25,000 kg | After tractor and trailer tare weight |
What types of semi-trailers are used in European road freight?
The most common semi-trailer in European road freight is the curtainsider — a flatbed frame with a fixed roof and sliding tarpaulin side curtains that open fully for forklift side-loading. Curtainsiders dominate European FTL and groupage movements because they accept loading from the side, the rear, and the top, with no structural interruption across the trailer floor.
Box body trailers have rigid fixed sides and a sealed cargo area, suited to high-value goods, pharmaceuticals, and electronics where weather protection and tamper evidence are required. Flatbed trailers carry no sides or roof — the right configuration for construction materials, steel coils, and oversized machinery that cannot be loaded through a standard trailer opening. Refrigerated trailers maintain a controlled temperature range for food, pharmaceutical, and perishable cargo.
Mega trailers provide 3.0 metres of internal height compared to 2.7 metres on a standard European trailer. The additional headroom serves high-volume light goods — packaged consumer products, textiles, automotive interior parts — where the limiting constraint is cubic capacity rather than axle weight. The curtainsider variant with a tensioned rather than sliding tarpaulin system is known as a tautliner, covered as a separate entry in the vehicle types glossary.
How does Go Trans use semi-trailer trucks in European freight?
Go Trans arranges full truckload freight across Europe using semi-trailer trucks through carrier partners DSV and DHL Freight. A full truckload consignment occupies one complete semi-trailer — one customer, one truck, one direct linehaul from the Belgian collection point to the European delivery address without intermediate consolidation.
DSV runs scheduled linehaul departures from Belgian terminals in Puurs, Rekkem, and Ghent using curtainsider and box body semi-trailers across lanes covering all EU member states. The 24,000 kg net payload of a standard semi-trailer truck suits industrial loads, machinery, manufacturing components, and full pallet consignments that exceed what groupage can accommodate on a single departure.
For loads that require a dedicated vehicle but fall below full truckload weight and volume thresholds, Go Trans arranges van delivery. For consignments that share trailer space with other customers on the same linehaul, Go Trans arranges LTL freight through the same DSV and DHL Freight road networks. FTL and LTL consignments both move as European road haulage on these lanes. Additional vehicle types, trailer specifications, and freight terminology are covered across the glossary of logistics terms.
Frequently Asked Questions
Why is it called a semi-trailer truck if the vehicle is very large?
The "semi" refers to the trailer — specifically its absence of a front axle. A semi-trailer is only partially supported by its own rear wheels. The front end rests on the tractor's fifth-wheel coupling rather than on its own axle. Because the trailer is a "semi-trailer," the full combination with the tractor is called a semi-trailer truck. The name describes axle configuration, not vehicle size.
What is the difference between a semi-trailer and a full trailer?
A semi-trailer has no front axle and cannot support its own front end — the front rests on the tractor's fifth-wheel or on the trailer's landing gear when uncoupled. A full trailer has both front and rear axles, carries its entire weight independently, and is towed by a rigid truck using a drawbar coupling. Full trailers are less common in European road freight because the semi-trailer truck combination offers better weight distribution and greater flexibility at loading terminals.
How many Euro pallets fit in a standard European semi-trailer?
A standard European semi-trailer floor accepts 33 Euro pallets (120 × 80 cm) in a single floor layer. Double-deck loading accommodates 66 Euro pallets where pallet height permits — typically for goods stacked below 60 cm. A mega trailer with 3.0 metres of internal height adds cubic capacity for the same footprint, suited to light high-volume goods where volume, not axle weight, is the binding constraint.