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CDL · Driving Combination Vehicles

Why should a combination vehicle driver increase following distance compared to a straight truck?

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

Because the longer, heavier combination requires more distance to stop, and the extra length and weight make sudden maneuvers more dangerous

  1. A Combination vehicles stop faster
  2. B Because the longer, heavier combination requires more distance to stop, and the extra length and weight make sudden maneuvers more dangerous
  3. C No reason
  4. D To save fuel

Why this is the answer

Combination vehicle drivers should increase FOLLOWING DISTANCE because the longer, heavier combination requires MORE distance and time to STOP, and the extra length/weight makes sudden maneuvers more dangerous (risk of skid/jackknife). CDL combination.

Following distance rule: at least 1 SECOND for every 10 FEET of vehicle length at speeds under 40 mph; ADD 1 second for speeds over 40 mph.

Example: a 60-foot combination at 50 mph needs at least 6 + 1 = 7 seconds. Increase further in bad weather, on downgrades, and when heavily loaded. The longer stopping distance (plus air brake lag) means the driver must look far ahead and leave generous space. Knowing to increase following distance for combination vehicles (and the 1-second-per-10-feet rule) is commonly tested.

Source: FMCSA CDL Manual — Combination, Following Distance

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About this topic: Driving Combination Vehicles

Off-tracking, jackknife risk, and rearward amplification mean a tractor-trailer behaves nothing like a single vehicle. Smooth inputs and conservative speed prevent the worst outcomes. This is one of 20 Combination Vehicles questions on driving combination vehicles, each with a full explanation on a single study page.

New to this exam? Our CDL exam guide explains the format, scoring, and how to prepare.

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