CDL · Driving Tank Vehicles

When driving a loaded tanker and approaching a curve, what is the primary danger related to tank design?

Correct answer

High center of gravity combined with liquid surge can cause the vehicle to roll over, especially in partially filled tanks where free liquid movement generates lateral forces in the turn

  1. A The tank will crack from road vibration
  2. B High center of gravity combined with liquid surge can cause the vehicle to roll over, especially in partially filled tanks where free liquid movement generates lateral forces in the turn
  3. C Tank vents may open and spill cargo
  4. D Steering becomes lighter in curves

Why this is the answer

Tanker rollover is the most common serious tanker accident type and is directly caused by the interaction of two factors: HIGH CENTER OF GRAVITY — liquid tankers have a much higher center of gravity than dry freight because all the weight is in a single cylindrical container high above the axles; LIQUID MOVEMENT — when a partially filled tank goes into a curve, the liquid can shift toward the outside of the turn, adding lateral momentum that makes rollover more likely than with a solid load of the same weight. CRITICAL NUMBERS: A tank that is 80% full or less is more dangerous than one that is completely full, because the liquid has room to surge; a full tank moves as a single unit, a partially filled tank allows the liquid to amplify the destabilizing forces; the worst fill level is typically 50-70%. SAFE DRIVING ADJUSTMENTS: Reduce speed significantly before entering curves — do not wait until you are in the curve to brake; take curves at well below the posted advisory speed (those speeds are for standard vehicles, not high-CG tankers); know your vehicle's specific center-of-gravity characteristics; never trust that your speed 'feels' safe — rollover happens suddenly without warning signs.
Source: FMCSA CDL Manual, Chapter 10, Tank Vehicles, High Center of Gravity

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