What is the signal to Release Air Brakes?

The signal to release air brakes is represented by the action of holding the signal arm at arm's length above the head. This position is distinct and clearly visible to the personnel operating the train, ensuring that it communicates unambiguously to all operators involved in the process.

The choice of positioning the arm above the head is significant because it establishes a strong visual signal that can be easily recognized. This is critical in operational scenarios where multiple signals are used, and clarity is paramount to maintaining safety and efficiency on the tracks. Holding the arm at this elevation minimizes the chance of misinterpretation that could lead to incorrect actions being taken by the crew.

All other choices listed do not conform to the standardized signaling protocol for releasing air brakes. For example, swinging a signal sideways may indicate a different command or action entirely, while pointing at the ground may not convey any actionable instruction. Similarly, raising the arm in a circular motion does not match the recognized practices for this signaling step and could confuse crew members. Hence, the clear and precise sign of holding the arm above the head stands out as the correct method for signaling the release of air brakes.