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CDL · General

What does the term 'dual air brake system' mean?

Correct answer

Two separate air brake systems (typically one for the front, one for the rear) that share one set of controls, providing a backup if one system fails

  1. A Two drivers operate the brakes
  2. B Two separate air brake systems (typically one for the front, one for the rear) that share one set of controls, providing a backup if one system fails
  3. C Brakes that work twice as hard
  4. D A system with no reservoirs

Why this is the answer

A DUAL AIR BRAKE SYSTEM has TWO SEPARATE air brake systems that use a single set of controls. CDL air brakes. Typically: one system operates the rear brakes, the other operates the front brakes; each has its own reservoirs, lines, and components. SAFETY/BACKUP: if one system fails (loses air), the OTHER system still provides braking (though with reduced capacity and longer stopping distance) — a redundancy/safety feature. Both systems must be charged (typically to about 100-125 psi) before driving. Modern heavy vehicles use dual air systems for this redundancy. Knowing the dual system provides backup braking if one part fails is commonly tested.
Source: FMCSA CDL Manual — Air Brakes, Dual System

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