Alabama CDL General Practice Test

An air pressure gauge shows the pressure available for braking. In an air-brake system, the braking power comes from compressed air stored in reservoirs, and the gauge on the dash tells you how much pressure you have to operate the brake chambers. Keeping an eye on this gauge is essential because low pressure means reduced braking effectiveness and can trigger warnings or protective actions. The other instruments measure fuel level, engine RPM, and miles driven, which don’t indicate braking pressure.