Which of the following best describes the role of pressure relief valves in an air brake system?

The role of pressure relief valves in an air brake system is to release excess air pressure. These valves are crucial for maintaining safety by preventing over-pressurization in the air brake system, which can lead to system failures or malfunctions. When the air pressure in the system exceeds a predetermined level, the pressure relief valve opens to allow some of the air to escape, thus reducing the pressure to a safe operating range. This mechanism ensures that the air brake system operates efficiently and safely, providing effective braking performance without the risk of damage due to excessive pressure.

In the context of the other options, storing excess air pressure is not the function of these valves; instead, they serve to prevent pressure buildup. Maintaining consistent braking pressure is related but is not the primary function of a pressure relief valve, which specifically deals with excess pressure rather than managing it under normal operating conditions. Lastly, regulating brake fluid levels does not apply to air brake systems, which operate using compressed air rather than hydraulic fluid.