What must be done before moving cars or locomotives?

Before moving cars or locomotives, it is essential to fully release all hand brakes. This is critical for safe train operation, as hand brakes are designed to hold cars in place and prevent them from rolling. If the hand brakes are not completely released, the train could experience difficulties moving, such as increased drag or unpredictable behavior when starting.

Releasing all hand brakes ensures that the train can move smoothly and safely, allowing for controlled acceleration and deceleration. It helps maintain stability in the train's movement and reduces the risk of accidents due to unexpected rolling or resistance from engaged brakes.

In contrast, activating hand brakes or having them partially released could hinder the train's ability to move. Reducing the throttle to IDLE and precharging the air brake system are also important steps in the process of preparing for movement, but they do not directly address the need to ensure that the hand brakes are fully off, which is vital for safe operations.