CDL Tank Braking with Empty, Full, Partial Loads — Questions and Answers
Question 1: A driver is hauling a tank that is only half full of liquid. What happens to the liquid when the driver brakes, and how should the driver brake?
- The liquid surges forward, so the driver should brake early and gradually (Correct answer)
- The liquid stays in place, so normal hard braking is fine
- The liquid surges backward, which helps slow the truck, so the driver can brake later
- The liquid settles to the bottom, so braking has no effect on the truck
Correct answer: The liquid surges forward, so the driver should brake early and gradually
Liquid in a partly filled tank moves forward when the truck brakes, and the surge pushes the truck ahead. The driver should brake early and gradually to keep it under control.
A partially filled tank leaves room for the liquid to move. When you brake, the liquid keeps moving forward, then sloshes back and forth. This surge can push the truck through the brake force you have applied. Look well ahead, slow early, and apply the brakes gradually and smoothly. Hard, late braking makes the surge worse and makes the truck harder to control.
Question 2: Compared with the same truck carrying a full load, an empty tank truck generally:
- Stops in a shorter distance because it is lighter
- Stops in the same distance because the brakes are identical
- Needs a longer distance to stop because it has less traction (Correct answer)
- Stops in a shorter distance only if the tank is baffled
Correct answer: Needs a longer distance to stop because it has less traction
Empty trucks take longer to stop than loaded ones because a lighter vehicle has less traction. Brakes designed for heavy loads can lock up or skid more easily when the truck is empty.
Brakes on heavy trucks are designed to stop a fully loaded vehicle. With no load, less weight presses the tires onto the road, so less traction is available. Wheels can lock up more easily and the stopping distance can be longer. Do not assume an empty tank is safer to stop. Leave extra following distance and brake smoothly.
Question 3: Which tank design lets liquid surge forward and backward the most when the driver brakes?
- A tank divided by bulkheads into separate compartments
- A tank with baffles
- A tank with a small outage
- A smooth bore tank (Correct answer)
Correct answer: A smooth bore tank
A smooth bore tank has no internal barriers, so the liquid can surge freely forward and back. This makes braking harder to control when it is partly full.
Smooth bore tanks, such as those used for food-grade products like milk, have no baffles or bulkheads. Liquid can move through the full length of the tank. The surge can be strong enough to push the truck, especially on slippery roads. A driver of a smooth bore tank that is not full must brake very early and very gently.
Question 4: A driver in a partly filled tank truck brakes hard on a wet road. The liquid surges forward. What is the most likely result?
- The surge pushes the truck forward and can carry it farther than the driver expects (Correct answer)
- The surge pushes the truck backward and shortens the stop
- The surge has no effect on a truck with working brakes
- The surge steers the truck gently toward the shoulder
Correct answer: The surge pushes the truck forward and can carry it farther than the driver expects
On a slippery surface, forward liquid surge can push the truck even with the brakes applied. The stop takes longer than the driver expects.
A large mass of liquid moving forward carries momentum. When the liquid hits the front of the tank, it pushes the truck forward. On wet or icy pavement, where tire grip is already limited, this push can overcome the traction available. The truck may slide through an intersection or into traffic. This is why a driver should slow down early and avoid sudden, hard stops.
Question 5: Which technique is best for slowing a tank truck that is carrying a partial load?
- Wait until the last moment, then brake as hard as possible
- Brake early and smoothly, and allow extra following distance (Correct answer)
- Pump the brake pedal repeatedly in short, hard bursts
- Shift to neutral and coast to a stop
Correct answer: Brake early and smoothly, and allow extra following distance
Braking early and smoothly, with extra following distance, keeps liquid surge to a minimum. It also gives the driver room to control the truck.
The harder and later you brake, the more violent the liquid surge. Smooth, early braking lets the liquid move gradually. Extra following distance gives you room to slow without sudden stops. Coasting in neutral is unsafe because it gives up engine braking and control. Repeated hard bursts of braking would also set the liquid sloshing.
Question 6: Which statement about stopping a tank truck is correct?
- Only a full tank affects the stopping distance
- Surge matters only for empty tanks
- Weight makes no difference to a truck's stopping distance
- Stopping distance depends on how much liquid is loaded and how it can move in the tank (Correct answer)
Correct answer: Stopping distance depends on how much liquid is loaded and how it can move in the tank
The amount of liquid and the freedom it has to move both change how the truck stops. Full, partial and empty loads each need different braking care.
A full tank has a lot of weight and needs a long distance to stop, but it has little room for surge. A partly filled tank has less weight but can surge forward and back. An empty truck has the least traction and may take longer to stop. A good tank driver adjusts speed, following distance and braking to the current load.
Question 7: Why does a tank that is completely full of liquid produce little surge when the truck brakes?
- Liquid becomes solid when the tank is full
- Baffles are not needed in a full tank
- The tank walls absorb all of the braking force
- There is almost no empty space for the liquid to move into (Correct answer)
Correct answer: There is almost no empty space for the liquid to move into
Surge needs room to move. A full tank leaves almost no outage space, so the liquid cannot slosh.
Liquid surge happens when a wave of liquid moves inside a tank with empty space above it. A completely full tank has very little outage, so the liquid mostly moves with the truck. Even so, a full tank is heavy, so it needs a longer distance to stop and has a high center of gravity. Many tank loads are only partially full, and these call for the most careful braking.
Question 8: A driver leaves a loading rack with a tank only one-third full of liquid. What is the best way to handle the first stop sign ahead?
- Brake lightly at the last second, since the load is small
- Apply the brakes very hard once to stop the sloshing
- Begin slowing well before the sign and brake gently throughout (Correct answer)
- Downshift to the lowest gear at high speed to stop the truck
Correct answer: Begin slowing well before the sign and brake gently throughout
A partly filled tank can surge, so the driver should start slowing early and brake gently. This keeps the liquid from pushing the truck.
A one-third load leaves plenty of room for liquid to surge. The weight is moderate, but the moving liquid can push the truck forward. Begin slowing early, use gentle steady brake pressure, and be ready for the surge as the truck comes to a stop. Hard braking at the last second would start a strong surge. Downshifting at high speed can damage the engine or drivetrain and may cause a skid.
Question 9: Baffles in a tank help the driver during braking mainly by:
- Reducing the forward and back movement of the liquid (Correct answer)
- Removing the need to brake gradually
- Increasing the tank's total capacity
- Stopping all side-to-side movement of the liquid
Correct answer: Reducing the forward and back movement of the liquid
Baffles are barriers with holes that slow the forward-and-back movement of the liquid. The liquid can still surge, though, so the driver must still brake with care.
A baffled tank has internal walls with openings that reduce front-to-back surge. They do not stop the liquid completely, and side-to-side movement can still happen, which affects rollover risk. Because a baffled tank can still surge, a driver must keep braking early and smooth. Bulkheads, which divide the tank into separate compartments, hold the liquid more tightly.
Question 10: Which load condition requires a tank driver to be MOST concerned about liquid surge during braking?
- A completely full tank
- A tank that is partially filled (Correct answer)
- A tank with no liquid and no residue
- A full tank with several bulkheaded compartments
Correct answer: A tank that is partially filled
A partly filled tank has space for the liquid to surge. Full tanks and bulkheaded compartments have little room for it, and an empty tank has nothing to surge.
Surge requires liquid and room to move. A full tank has almost no room, and an empty tank has no liquid to move. A partly filled tank has both, so it creates the strongest surge when you brake. Drivers should slow early and brake gradually with a partial load. Bulkheads reduce the problem by splitting the load into small separate compartments.
CDL Tank Braking with Empty, Full, Partial Loads
A driver is hauling a tank that is only half full of liquid.
What happens to the liquid when the driver brakes, and how should the driver brake?
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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