What is the primary purpose of coupling devices in trucks?

The primary purpose of coupling devices in trucks is to connect the service and emergency air lines. This is crucial because the service air line is responsible for the regular brake systems, while the emergency air line is essential for ensuring that the trailer's brakes are engaged in the event of a separation from the tractor. Proper connection of these lines ensures that the braking systems operate effectively, enhancing safety during operation.

While securing the trailer to the tractor is also an important function of coupling devices, it primarily refers to mechanical coupling, whereas the connection of air lines specifically addresses the functionality and safety of the braking system. Enhancing fuel efficiency and providing electrical connections are relevant to truck operation in various contexts but are not the primary function of coupling devices. Thus, connecting the air lines is central to ensuring that the entire braking system functions reliably and safely during transit.