Draft forces are present when a train is in which condition?

Draft forces are primarily associated with a slack-stretched condition. In this scenario, as the couplers between cars are under tension, the force is applied to pull the cars closer together. This tension creates a draft force, which is necessary for the train to maintain its movement in a unified manner. When the train is slack-stretched, the individual cars are being actively pulled, and the effect of draft forces becomes significant as they come into play during acceleration and movement.

In contrast, conditions such as being fully loaded or on a downhill gradient may involve different dynamics, such as the weight of the cargo impacting braking or sheer gravitational pull affecting train speed. Slack-bunched conditions, on the other hand, involve a loose arrangement of the couplings between cars, which typically produces different forces and can lead to compression, but does not effectively convey a draft force as they are not under tension. Thus, slack-stretched is the most accurate condition for the presence of draft forces.