What defines a full jackknife?

A full jackknife occurs when the angle between the tractor and the trailer increases to a critical point, leading to a scenario where they can form an angle of 90 degrees or more. This situation typically arises when the trailer swings out away from the tractor, often due to sudden braking or acceleration. When the angle exceeds a certain threshold, it can create a hazardous situation as it compromises the stability and control of the vehicle combination.

The other options, while potentially related to issues that can arise in trucking situations, do not accurately define a full jackknife. For instance, the detachment of the trailer from the tractor signifies a disconnected or uncoupled situation rather than a full jackknife. Excessive tire wear may indicate mechanical issues or improper loading but does not describe the specific mechanics of a jackknife incident. Similarly, an unbalanced load can contribute to instability, but it does not encapsulate the definition of a full jackknife situation. Recognizing the specific mechanics and characteristics of a jackknife incident is crucial for drivers to avoid such scenarios on the road.