Which of the following requires vehicles to travel at a speed of 5 MPH?

Vehicles towing aircraft are required to travel at a speed of 5 MPH primarily for safety reasons. Towing operations involve large, often heavy aircraft that can be vulnerable to damage if subjected to sudden movements or high speeds. A slower speed helps ensure that the operator has better control of the aircraft's movement, reducing the risk of accidents or collisions on the airfield.

Additionally, maintaining a speed of 5 MPH helps protect other personnel, equipment, and vehicles in the vicinity, as well as ensuring that the aircraft being towed does not create a hazard due to its size and weight. This speed limit is a crucial part of airfield safety protocols that aim to minimize risks in a high-traffic environment where many activities are occurring simultaneously, such as maintenance, passenger transport, and security operations. While other activities also have specific speed requirements, the emphasis on 5 MPH for towing aircraft is particularly significant due to the associated risks.