What are vehicles designed to run upon highways and pulled by motor vehicles classified as?

The classification of vehicles designed to run upon highways and pulled by motor vehicles as "motor vehicles" is accurate because this term encompasses all vehicles that are used for transportation and are typically powered by an engine or motor. In this context, when referring to vehicles being pulled, it indicates that they are reliant on another motor vehicle for propulsion, yet they are still recognized under the wider definition of motor vehicles due to their design for highway use.

This classification often includes trailers or semi-trailers that may not be self-propelled but are essential components of the motor vehicle system, especially in commerce and logistics. These vehicles are subject to the same laws and regulations that govern other motor vehicles, ensuring that they meet safety and operational standards for use on public roads.

On the other hand, other classifications such as motorized trailers, utility vehicles, and pedal vehicles do not encompass the broad definition indicated in the question, making them less fitting for this context. Motorized trailers specifically refer to a certain type of trailer that may have its own propulsion system, while utility vehicles and pedal vehicles cater to different uses and operational mechanisms altogether. Thus, the classification of these highway-bound, towed vehicles as "motor vehicles" is the most accurate and applicable choice.