What feature must all vehicles equipped with air brakes have?

All vehicles equipped with air brakes are required to have a low pressure warning signal as an essential safety feature. This system is crucial because it alerts the driver when the air pressure in the brake system falls below a safe operating level, typically around 60 psi. If pressure drops too low, the air brakes can become ineffective, which can lead to a loss of braking power and increase the risk of accidents.

The low pressure warning signal typically consists of an audible alarm or a visual indicator, such as a light on the dashboard, which prompts the driver to take immediate action. Ensuring that this warning system is operational helps maintain safe driving conditions and mitigates the risks associated with air brake system failures.