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CDL · Antilock Brake Systems

Which combination vehicles are required to have ABS?

Reviewed by Jordan Morley, Editorial Lead at 247SimpleTests. Written by the 247SimpleTests Editorial Team from the official source material cited on every question.

Correct answer

Tractors built since March 1997 and trailers built since March 1998

  1. A Only tractors
  2. B All combination vehicles regardless of age
  3. C Tractors built since March 1997 and trailers built since March 1998
  4. D Only trailers built after a certain date

Why this is the answer

Federal regulations require ABS on air-braked tractors built on or after March 1, 1997, and on air-braked trailers built on or after March 1, 1998. Hydraulic-braked vehicles have similar requirements. Vehicles built before these dates are not required to have ABS, but many have been retrofitted. An ABS-equipped vehicle has a yellow ABS warning light that comes on briefly at startup and goes out once the system has self-tested; a steady or recurring yellow ABS light indicates a malfunction. ABS prevents wheel lockup during heavy braking, preserving steering control and often reducing stopping distance on slick surfaces. Drivers should brake firmly with ABS, not pump the brakes.
Source: FMCSA CDL Manual 6.5.1 Antilock Brake Requirements

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About this topic: Antilock Brake Systems

ABS prevents wheel lockup during heavy braking, preserving steering and reducing stopping distance on slick surfaces. Drivers must brake firmly, not pump, on ABS-equipped vehicles. This is one of 6 Combination Vehicles questions on antilock brake systems, each with a full explanation on a single study page.

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