Semi-trailer truck

A semi-trailer truck is a specific combination of two vehicle components used in heavy-duty freight transport. Unlike a conventional truck-trailer combination, it does not consist of a truck with a separate trailer, but rather of a towing unit and a transport container mounted on top of it.

The Components: Tractor and Semi-Trailer

The distinctive feature of the semi-trailer truck lies in its modular design. It consists of two main components:

• Tractor unit (SZM): a short chassis that comprises only the cab, the engine, and the fifth wheel. It does not have its own cargo area.
• The semi-trailer has only rear axles. Since it has no front axle, it cannot stand on its own but rests on the tractor’s fifth wheel at the front.

Mechanics of the Connection

The two parts are connected via the kingpin on the trailer, which locks into the tractor’s fifth-wheel coupling. A significant portion of the trailer’s weight is thus borne directly by the tractor’s drive axle. This ensures high traction and stability while driving. When uncoupling the trailer, extendable support jacks at the front of the trailer prevent it from tipping forward.

Logistical Advantages in Practice

The use of semi-trailer trucks offers freight forwarders and logistics centers significant advantages over conventional articulated trucks:

• Flexibility through two-way traffic: A tractor unit can drop off a full semi-trailer at the destination and immediately pick up a pre-loaded, ready-to-go trailer for the return trip. This means the tractor unit does not have to wait for the cargo to be loaded or unloaded.
• Easy maneuvering: Since a semi-trailer truck has only one pivot point (the fifth wheel), it is much easier to steer in reverse up ramps or into narrow loading bays than a combination with multiple joints.
• Loading capacity: Semi-trailers offer a continuous loading area without any interruption between the tractor unit and the trailer. This makes it much easier to transport bulky goods or long loads.

Regulatory Requirements

In Germany, a standard semi-trailer truck with more than 4 axles generally may not exceed a gross vehicle weight of 40 tons. The maximum total length of the combination is limited to 16.50 meters. The trailer’s loading area typically has a standard length of 13.60 meters.