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CDL · Outage and Loading

How does the density of the liquid affect how much you can legally load?

Correct answer

Tanks have a fixed volume, but maximum legal weight by axle and gross combination limits how much of a denser liquid you can actually load

  1. A Density has no effect on legal load
  2. B Tanks have a fixed volume, but maximum legal weight by axle and gross combination limits how much of a denser liquid you can actually load
  3. C Density only affects fuel mileage
  4. D Density determines required placard color

Why this is the answer

A tank has a fixed volume but no fixed legal weight — weight depends on the density of the contents. Water weighs about 8.3 lb/gallon; gasoline about 6.2 lb/gallon; molasses about 12 lb/gallon; mercury (rare hazmat load) about 113 lb/gallon. A tank filled with a dense liquid hits legal weight limits long before the volume is full. Drivers must calculate the maximum legal load: federal interstate gross combination limit is 80,000 lbs without permits, with individual axle limits (typically 12,000 lbs steering, 34,000 lbs drive tandem, 34,000 lbs trailer tandem). The shipper usually calculates this, but the driver shares responsibility for not exceeding weight at any axle.
Source: FMCSA CDL Manual 8.3.3 Weight and Density

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