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CDL · Inspecting Combination Vehicles

What is the most common safety hazard when uncoupling a trailer on a soft surface?

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

The landing gear sinking into the surface and the trailer dropping

  1. A Tire damage
  2. B Cargo theft
  3. C Battery drain
  4. D The landing gear sinking into the surface and the trailer dropping

Why this is the answer

When uncoupling a trailer on soft surfaces — wet ground, asphalt softened by heat, gravel, or unpaved lots — the landing gear can sink into the surface under the trailer's weight, causing the trailer to drop after the tractor pulls out. This can damage the trailer, cargo, and surrounding property, and can injure people. Prevention: park trailers on hard, level surfaces whenever possible. On softer surfaces, place landing gear feet on wide boards or steel plates to spread the load. Avoid parking on grades; if you must, chock the wheels in both directions. After lowering landing gear, look to confirm it is firmly contacting the ground before disengaging the fifth wheel.
Source: FMCSA CDL Manual 6.2.8 Uncoupling Safely

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About this topic: Inspecting Combination Vehicles

The combination-vehicle inspection adds fifth wheel, kingpin, glad hands, and trailer-specific items to the standard pre-trip routine. This is one of 13 Combination Vehicles questions on inspecting combination vehicles, each with a full explanation on a single study page.

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