What is a self-propelled power unit connected to a series of trailers called?

A self-propelled power unit connected to a series of trailers is accurately described as a tractor-trailer train. This term specifically refers to the combination of a tractor unit (which is the powered vehicle) and one or more trailers that it pulls. The tractor provides the necessary power and maneuverability, while the trailers are designed to carry cargo or goods.

In logistics and transportation, this configuration is common because it allows for the efficient movement of large quantities of goods over long distances. The tractor-trailer system is versatile and can be used for various types of cargo, making it a key component in supply chain operations.

The other options do not correctly represent this configuration. A forklift train refers to a system used for moving goods but involves forklifts rather than a combination of a tractor and trailers. A delivery truck generally refers to a standalone vehicle for transporting goods but does not describe the connection between a powered unit and trailers. Similarly, a transport vehicle is a broader term that could refer to any vehicle used for moving items but lacks the specific definition of a tractor-trailer train.