What needle color indicates brake pipe pressure on the duplex air pressure gauge?

Answer: C — White

The needle color that indicates brake pipe pressure on the duplex air pressure gauge is white. This color coding is standardized to help operators quickly identify the various readings on the gauge. The white needle specifically points to the brake pipe pressure, allowing for efficient monitoring of the brake system's status during operations. Understanding the importance of recognizing these indicators is crucial for safe train operations. The gauge readings allow train operators to manage air brake pressure effectively, which is vital for both performance and safety. Familiarity with color coding assists in rapid assessments during inspections or operations, ensuring that any necessary adjustments can be made in a timely manner.