What must all vehicles with air brakes have?

All vehicles equipped with air brakes are required to have a low air pressure warning signal. This safety feature is crucial because it alerts the driver when the air pressure in the braking system falls below a certain threshold, which can indicate a loss of brake function. Since air brakes rely on compressed air to operate effectively, maintaining an adequate air pressure level is essential for safe braking performance. If the pressure drops too low, it could lead to brake failure, significantly increasing the risk of accidents.

While other features like an automatic brake adjustment system or a secondary braking system may enhance safety or convenience, the low air pressure warning signal is mandated as a fundamental requirement to ensure that drivers are aware of potential issues with their braking system promptly.