CDL Tank Cargo Surge — Questions and Answers
Question 1: A tank vehicle is carrying a partially filled load. What is "liquid surge"?
- Movement of the liquid back and forth or side to side inside the tank (Correct answer)
- The pressure that builds in the tank as the liquid warms
- The extra weight the tank carries when the liquid expands
- The liquid foaming from vibration on rough roads
Correct answer: Movement of the liquid back and forth or side to side inside the tank
Liquid surge is the movement of liquid in a partly filled tank, forward and backward or side to side. It happens when the vehicle accelerates, brakes, or turns.
A liquid in a partly filled tank is free to move whenever the vehicle changes speed or direction. When you brake, the liquid rushes forward. When you accelerate, it moves back. In a turn or lane change it moves to the side. This shifting load changes how the vehicle handles and can push the vehicle in directions the driver does not expect.
Question 2: Which tank design allows the most liquid surge?
- A tank divided into compartments by bulkheads
- A baffled tank
- A tank that is filled completely
- A smooth-bore tank with no baffles (Correct answer)
Correct answer: A smooth-bore tank with no baffles
A smooth-bore tank has nothing inside to slow the liquid, so it allows the most severe surge. Baffles and bulkheads restrict movement.
Smooth-bore tanks have no internal walls, so the liquid can move freely from front to back and side to side. They are common for hauling products such as milk, because the smooth interior is easy to clean. Because surge is strongest in these tanks, the driver must be especially gentle with the brake, accelerator, and steering.
Question 3: A baffled tank is partly full. Which statement about surge in it is correct?
- Baffles remove all surge, so side-to-side movement is no concern
- Baffles help control front-to-back surge, but side-to-side surge can still occur (Correct answer)
- Baffles stop side-to-side surge but not front-to-back surge
- Baffles make surge worse when the tank is less than half full
Correct answer: Baffles help control front-to-back surge, but side-to-side surge can still occur
Baffles have holes in them and mainly slow forward-and-back surge. Side-to-side surge can still happen, and it can contribute to rollovers.
Baffles are walls with openings that slow the liquid's movement from front to back. They do little to stop the liquid shifting from side to side. A driver who takes a curve or makes a lane change too fast in a baffled tank can still start a dangerous sideways surge and roll the vehicle.
Question 4: What is the main reason a compartmented (bulkheaded) tank reduces surge?
- The compartments let the driver use the liquid in a set order
- The bulkheads make the tank walls thicker and the vehicle heavier
- The compartments lower the liquid's temperature
- Each compartment is a separate tank, so the liquid cannot surge along the whole length (Correct answer)
Correct answer: Each compartment is a separate tank, so the liquid cannot surge along the whole length
Bulkheads divide the tank completely, so each compartment acts as a separate tank. Liquid can only surge within its own compartment.
Unlike baffles, which have holes, bulkheads completely separate the tank into sections. Liquid cannot move from one compartment to the next, so a surge can only build up over the short length of a single compartment. A partly filled compartment can still surge inside itself.
Question 5: A driver brakes hard on a slippery road with a partly filled smooth-bore tank. What can happen as the vehicle slows?
- The liquid stays still and the stopping distance gets shorter
- The liquid surges forward and can push the vehicle ahead, increasing stopping distance (Correct answer)
- The liquid drops its density and the vehicle stops sooner
- The liquid surges away from the cab and presses the rear tires down
Correct answer: The liquid surges forward and can push the vehicle ahead, increasing stopping distance
When you brake, the liquid moves forward and its momentum can push the vehicle ahead. On a slippery surface this can lengthen the stop.
Braking slows the vehicle, but the liquid keeps moving forward until it hits the front of the tank. The force of that surge pushes the vehicle forward, and the effect is worse on slippery roads. A driver should brake early and gently, and leave extra following distance.
Question 6: Which action best lowers the risk of surge-related rollover when you approach a curve in a partly filled tank?
- Hold your speed and steer sharply in the curve
- Slow down before the curve, then steer smoothly through it (Correct answer)
- Brake hard while in the middle of the curve
- Shift down in the curve so the engine slows the vehicle
Correct answer: Slow down before the curve, then steer smoothly through it
Reduce speed before the curve and steer smoothly. Hard steering or braking in a curve starts a side-to-side surge that can tip the vehicle.
Liquid cargo raises the vehicle's center of gravity and can swing sideways in a turn. Slowing down before the curve means you do not need to brake or change gears in it. Smooth steering keeps the liquid from sloshing hard against one side of the tank, and that reduces the rollover risk.
Question 7: Which load condition produces the least liquid surge?
- A tank filled to about half
- A tank filled to about one-quarter
- A tank filled completely, within legal weight limits and with outage allowed for expansion (Correct answer)
- A tank that has just been emptied by half and then refilled
Correct answer: A tank filled completely, within legal weight limits and with outage allowed for expansion
Surge needs empty space in which the liquid can move. A tank filled as full as is safe leaves little room, so it has little surge. Some outage is still left for expansion.
A liquid can only slosh when there is open space in the tank. A tank that is nearly full has almost none, so it has very little surge. A tank is still never filled completely, because the liquid expands as it warms and needs outage space. The most surge-prone loads are the ones that are only partly full.
Question 8: You haul a very dense liquid, such as some acids. Why are such loads often carried in a tank that is only partly full?
- Dense liquids need a lot of empty space to cool
- A full tank of a dense liquid could exceed legal weight limits (Correct answer)
- Dense liquids cannot surge, so a partly full tank is safe
- Dense liquids must be kept below the baffles
Correct answer: A full tank of a dense liquid could exceed legal weight limits
A dense liquid weighs more per gallon, so a full tank can be overweight. Partial loads are common, which means surge must be managed even though the tank is not full.
Liquid cargo varies a great deal in density. A full tank of a dense product can exceed legal weight limits, so the tank is often only partly filled. That leaves space for surge. Because dense liquids carry more momentum, the surge forces are stronger, and the driver has to be even more careful with braking and turns.
Question 9: Compared with a light liquid, a dense liquid in the same partly filled tank, moving at the same speed, will generally:
- Carry more momentum, so its surge pushes harder on the vehicle (Correct answer)
- Surge with less force, because heavy liquids cannot move
- Make no difference to handling, because only the volume matters
- Surge only front to back and never side to side
Correct answer: Carry more momentum, so its surge pushes harder on the vehicle
Momentum depends on mass. The same volume of a denser liquid has more mass and delivers a stronger push when it surges.
A denser liquid has more mass per gallon, so when it moves, it carries more momentum. When it surges against the end or side of the tank, it pushes harder on the vehicle than a lighter liquid would. Drivers must therefore treat a dense, partly filled load with extra care, and brake and turn more gently.
Question 10: A tank truck is partly full, and the driver starts off from a stop by accelerating briskly. What is the most likely effect of the surge?
- The liquid moves toward the rear, and the surge can rock the vehicle back and forth (Correct answer)
- The liquid stays in place and the vehicle accelerates normally
- The liquid moves up into the dome, and the pressure relief valve opens
- The liquid moves toward the front, and the drive wheels get more traction
Correct answer: The liquid moves toward the rear, and the surge can rock the vehicle back and forth
On acceleration the liquid shifts toward the rear, then rebounds forward. The back-and-forth movement can make the vehicle surge and hard to control.
When a tank accelerates, the liquid at first lags toward the rear. It then rebounds toward the front, and the cycle can repeat. This rocking effect makes the vehicle feel like it is pushing and pulling. Accelerating smoothly and gradually helps keep the surge small.
CDL Tank Cargo Surge
A tank vehicle is carrying a partially filled load.
What is "liquid surge"?
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Sources & references
Exam facts on this page (fees, format, dates, passing scores) are checked against these official sources; the date is our last check. Editorial policy
- dps.texas.gov — Eligibility · verified Nov 2026
- ecfr.gov — Eligibility, exam format, passing score · verified Nov 2026