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CDL · Outage and Loading

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

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

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 only affects fuel mileage
  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 determines required placard color
  4. D Density has no effect on legal load

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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About this topic: Outage and Loading

Outage is the space left in a tank so the liquid can expand as it warms; loading questions ask how much to leave, why it depends on the product, and how weight limits can be reached before the tank is full. This is one of 11 Tanker questions on outage and loading, each with a full explanation on a single study page.

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