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CDL · Driving Tank Vehicles

How does liquid surge affect stopping a tanker, and what should the driver do?

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

Surge can push the stopped tanker forward (the liquid wave continues moving after the truck stops), so the driver must allow extra stopping distance, brake smoothly and early, and be aware the vehicle may lurch forward when stopping

  1. A The driver should brake as hard as possible
  2. B Surge helps the tanker stop faster
  3. C Surge has no effect on braking
  4. D Surge can push the stopped tanker forward (the liquid wave continues moving after the truck stops), so the driver must allow extra stopping distance, brake smoothly and early, and be aware the vehicle may lurch forward when stopping

Why this is the answer

Surge and stopping: When a tanker brakes to a stop, the liquid continues moving forward as a wave, then surges back and forth.

Effects: The forward surge can PUSH the truck forward even after it has stopped — potentially into an intersection or the vehicle ahead; the surge makes the stop less predictable and can cause the vehicle to lurch.

Driver response: Allow EXTRA stopping distance (the surge effectively increases stopping distance); brake SMOOTHLY and EARLY (gradual braking reduces the surge wave compared to hard braking); anticipate stops well in advance; be ready for the vehicle to move forward slightly when it 'stops'; keep extra space ahead; SMOOTH BORE tanks (no baffles) have the most surge and require the most caution; on SLIPPERY roads, surge plus reduced traction is especially dangerous; the driver must mentally account for the fact that the liquid keeps moving after the truck stops; smooth, early, gradual braking with extra following distance is the key to safe tanker stopping.

Source: FMCSA CDL Manual — Tanker Braking and Surge

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About this topic: Driving Tank Vehicles

Driving a tank vehicle means managing a high centre of gravity and a shifting load: slow for curves well below the posted speed, brake early and smoothly, and never make sudden steering changes. These questions cover the handling rules for liquid loads. This is one of 21 Tanker questions on driving tank 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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