What is the advantage of a dual air brake system?

A dual air brake system has two completely separate air brake systems on the same vehicle, typically split between the front axle and the rear axles. Each system has its own air tanks, lines, and controls. If one system fails (a broken line, for example, or a leak), the other system continues to function and can stop the vehicle. Dual systems are required by federal regulations on most heavy commercial vehicles. The build-up time for both systems should be within the same range (50 to 90 psi within about 3 minutes for a typical truck) and pressure should be checked before every trip. The two air pressure gauges in the cab show each system's pressure separately so the driver can see if one fails.