A power-only truck, also known as a power unit or power-only unit, refers to a trucking arrangement where a tractor (the truck's front part that includes the engine and driver's cabin) is used to pull a trailer that belongs to someone else. In this setup, the owner of the tractor provides the driving power, while the trailer, which may contain cargo, belongs to a different entity, such as a shipping company, logistics provider, or trailer owner.

Power-only trucks are often used in situations where companies have an excess of trailers but need more tractors to transport them. This arrangement allows for more flexibility in managing assets and can be particularly useful during peak shipping seasons or when there's a need to move trailers between different locations.

As for the dimensions of power-only trucks (the tractors), they generally adhere to the same size standards as other commercial trucks in the USA. The most common dimensions for a tractor are:

Length: Varies depending on the configuration and type of tractor. Standard semi-truck tractors are typically around 70 to 80 feet (21 to 24 meters) when connected to a standard 53-foot trailer.
Width: The standard width of a commercial truck, including the tractor, is about 8 feet 6 inches (2.59 meters).
Height: Generally falls within the range of 12 to 14 feet (3.66 to 4.27 meters), though specific heights can vary based on the type of tractor and any additional equipment on the roof.

It's important to note that regulations and restrictions on truck dimensions can vary by state and region. Some regions might have stricter rules for overall length, weight, and height, while others might have special provisions for certain types of trucks or routes.

Power-only trucks play a crucial role in optimizing the efficiency and flexibility of logistics operations by ensuring that trailers are continuously in motion, even if the trailers and tractors are owned by different parties. This arrangement helps streamline the movement of goods and contributes to the overall effectiveness of the transportation industry.