What is the purpose of safety chains on a heavy trailer?

The purpose of safety chains on a heavy trailer is to prevent the trailer from detaching from the towing vehicle. These chains serve as a critical safety measure that keeps the trailer connected to the tow vehicle in the event that the hitch fails or becomes unlatched. If the trailer were to become detached, the safety chains would help secure it in place, minimizing the risk of accidents and ensuring that the trailer remains controlled instead of rolling freely, which could pose a danger to other road users.

The other options do not accurately reflect the function of safety chains. Quick adjustments during towing are managed through other means, and safety chains are not designed to improve aerodynamic efficiency or increase the load capacity of the trailer. Therefore, the primary and essential role of safety chains is indeed to enhance safety by securing the trailer to the towing vehicle.