Which of the following colors indicates the emergency line in a color-coded air brake system?

Answer: B — Red

In a color-coded air brake system, the emergency line is indicated by the color red. This standardization is important as it allows for immediate recognition and understanding of the system components, particularly in emergency situations. The red color is universally associated with emergency signals, making it clear that this line is crucial for the safe operation of the braking system. Understanding the role of the emergency line is key; it is responsible for delivering air to the brake chambers and is activated in case of a loss of air pressure in the system, engaging the brakes to stop the vehicle. This comprehension ensures that operators can identify and respond appropriately to any issues that may arise within the system, thus enhancing safety and operational effectiveness.