tractortrailers

Tractor-trailers, also known as semi-trucks or tractor-trailers, are a class of heavy goods vehicles used to haul freight. The vehicle consists of a tractor unit, which contains the engine and cab, and a non-powered trailer that carries cargo. The two parts connect by a fifth-wheel coupling on the tractor and a kingpin on the front of the trailer. This semi-trailer arrangement means the trailer’s weight is partially supported by the tractor and the wheels at the back, enabling long combinations of vehicle and trailer.

A typical tractor-trailer handles long-haul freight and can range from 28 to 53 feet in trailer length. In the United States, the common gross vehicle weight rating is about 80,000 pounds when fully loaded, though limits vary by jurisdiction. The trailer types include dry vans, refrigerated units (reefers), flatbeds, curtain-sided trailers, tankers, and container chassis; the dry van is the most widely used for general freight.

Operation requires appropriate licensing; in the United States and Canada, this is usually a Class A commercial driver's license, along with hours-of-service regulations that govern driver duty periods and rest breaks. Heavy trucks are equipped with air braking systems, anti-lock braking, electronic stability controls, and underride guards in many regions, with periodic inspections.

Historically, tractor-trailer combinations emerged in the early to mid-20th century with advances in trucking and standardization of trailer dimensions, enabling highway transport and intermodal movement. Today, they remain a core modality for global freight transport, balancing payload, efficiency, and regulatory compliance.