How many aft restraint devices must be installed before a vehicle is left unattended?

Before a vehicle is left unattended, it is essential to ensure that the proper measures are taken to secure it. Installing one aft restraint device is the minimum requirement to provide adequate security and prevent any unintended movement of the vehicle. This helps to stabilize and hold the vehicle in place, reducing the risk of accidents or damage that could occur if the vehicle were to roll or shift unexpectedly.

One aft restraint device is typically enough to ensure the vehicle is adequately secured while allowing for a balance of safety and practicality. Additional restraints may enhance security, but the requirement calls for at least one to meet safety protocols and industry guidelines. Therefore, the correct answer reflects the essential minimum level of restraint that ensures safety without unnecessarily complicating the process of securing the vehicle.