What characterizes a tractor jackknife?

A tractor jackknife is characterized by the situation where the drive tires lock and the tractor starts to spin sideways. This occurs when the rear wheels of the tractor lose traction, often due to excessive braking or slippery road conditions, leading to a loss of control. The tractor then pivots at the hitch, creating an acute angle between the tractor and the trailer, resembling a jackknife.

This phenomenon poses significant dangers as it can lead to a complete loss of vehicle control and increases the risk of collision and damage. Understanding this type of accident is crucial for drivers, as it can help them recognize the signs and take preventive measures, such as maintaining safe speeds and proper braking techniques.

The other options describe different scenarios that do not accurately represent a jackknife situation. For example, while trailer spins can occur, it generally does not capture the essence of a tractor jackknife specifically. The inability of the truck to stop and load shifting might be related to truck accidents but are distinct from the actual mechanics of a jackknife incident.