CDL Tank Vehicle (N) Endorsement Knowledge Test — Questions and Answers

Question 1: A DOT-specification cargo tank must have an external visual inspection and leakage test at least how often?

Every year (Correct answer)
Every 2 years
Every 5 years
Every 6 months

Correct answer: Every year

Under 49 CFR 180.407, DOT-specification cargo tanks need an external visual inspection and leakage test at least once each year. The longer 5-year interval applies to pressure retests, not to these checks.

Question 2: Which type of tank has no internal barriers to slow the movement of liquid?

Cargo-baffled tank
Smooth bore tank (Correct answer)
Baffled tank
Compartmented tank

Correct answer: Smooth bore tank

A smooth bore tank has nothing inside to slow liquid movement. Its liquid surges freely from end to end.

Question 3: 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 backward, which helps slow the truck, so the driver can brake later
The liquid stays in place, so normal hard braking is fine
The liquid settles to the bottom, so braking has no effect on the truck
The liquid surges forward, so the driver should brake early and gradually (Correct answer)

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.

Question 4: Which load condition produces the least liquid surge?

A tank filled completely, within legal weight limits and with outage allowed for expansion (Correct answer)
A tank filled to about half
A tank that has just been emptied by half and then refilled
A tank filled to about one-quarter

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.

Question 5: Which statement about baffles is correct?

Baffles remove the need to slow down on curves
Baffles divide the tank into separate sections that never share liquid
Baffles are bulkheads with holes that slow the movement of the liquid (Correct answer)
Baffles are what make a tank a smooth bore tank

Correct answer: Baffles are bulkheads with holes that slow the movement of the liquid

A baffle is a bulkhead with holes in it. It slows liquid movement but does not stop it.

Question 6: Compared with a light liquid, a dense liquid in the same partly filled tank, moving at the same speed, will generally:

Surge with less force, because heavy liquids cannot move
Surge only front to back and never side to side
Carry more momentum, so its surge pushes harder on the vehicle (Correct answer)
Make no difference to handling, because only the volume matters

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.

Question 7: A driver brakes hard on a slippery road with a partly filled smooth-bore tank. What can happen as the vehicle slows?

The liquid drops its density and the vehicle stops sooner
The liquid surges forward and can push the vehicle ahead, increasing stopping distance (Correct answer)
The liquid stays still and the stopping distance gets shorter
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.

Question 8: A tank vehicle is carrying a partially filled, smooth-bore (unbaffled) tank. What is the main hazard of the liquid in this tank during braking and acceleration?

The liquid turns to vapor and lowers the tank's weight
The liquid surges forward and backward, which can push the vehicle (Correct answer)
The liquid stays fixed in place and shifts the load only sideways
The liquid freezes and blocks the outlet valves

Correct answer: The liquid surges forward and backward, which can push the vehicle

Liquid in a partly filled smooth-bore tank sloshes back and forth freely when you speed up or brake. That surge can push the vehicle in the direction the liquid is moving.

Question 9: A driver of a smooth bore tank slows quickly on a flat road and feels the truck being pushed forward. What is causing this?

Liquid surging toward the front of the tank (Correct answer)
Liquid pressure dropping inside the tank
Vapor expanding inside the compartments
The tank's baffles trapping air

Correct answer: Liquid surging toward the front of the tank

In a smooth bore tank, braking sends the liquid surging forward, and it can push the truck. Nothing inside the tank stops the movement.

Question 10: A driver is moving from a baffled tank to a smooth bore tank. Which change in driving is most appropriate?

Accelerate more quickly to keep the liquid settled
Brake later because the liquid helps slow the vehicle
Brake earlier and more gently, and allow more stopping distance (Correct answer)
Use the same following distance as with the baffled tank

Correct answer: Brake earlier and more gently, and allow more stopping distance

Smooth bore tanks have stronger surge, so braking should start sooner and be gentler. More following distance is needed.

Question 11: A tank vehicle has several separate compartments divided by bulkheads. What is the main effect of the bulkheads on liquid movement?

They raise the center of gravity so the vehicle handles better in curves
They allow liquid to flow freely from one compartment to the next
They remove the need to watch speed on curves
They stop liquid from moving between compartments, which limits surge within each compartment (Correct answer)

Correct answer: They stop liquid from moving between compartments, which limits surge within each compartment

Bulkheads divide the tank into separate compartments, so liquid cannot flow between them. Each compartment holds a smaller volume, which limits how much surge can build.

Question 12: What is the main reason to leave outage (empty space) when filling a tank with a liquid that expands when warmed?

To reduce the weight on the axles
To make the tank easier to clean
To prevent static electricity from forming
To allow room for the liquid to expand without overfilling or leaking (Correct answer)

Correct answer: To allow room for the liquid to expand without overfilling or leaking

Liquids expand as they warm, so the outage gives the product room to grow. Without it, the tank could overflow or be stressed.

Question 13: What is the main purpose of baffles inside a tank?

To raise the load's center of gravity
To make the tank easier to clean
To slow the liquid's forward-and-back surge (Correct answer)
To keep different liquids in separate sections

Correct answer: To slow the liquid's forward-and-back surge

Baffles are walls with holes in them. They let liquid pass through but slow its forward-and-back movement.

Question 14: Which technique is best for slowing a tank truck that is carrying a partial load?

Shift to neutral and coast to a stop
Pump the brake pedal repeatedly in short, hard bursts
Brake early and smoothly, and allow extra following distance (Correct answer)
Wait until the last moment, then brake as hard as possible

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.

Question 15: Compared with a fully loaded, completely filled tank, why can a half-filled tank be harder to control when you brake?

The air in the tank pulls the vehicle backward
The liquid has room to move, and its surge pushes the vehicle as you brake (Correct answer)
Half-filled tanks have more traction on the drive axles
The brakes fade faster when a tank is half empty

Correct answer: The liquid has room to move, and its surge pushes the vehicle as you brake

A partly filled tank gives the liquid room to move, so braking sends a wave of liquid forward that pushes the vehicle. A full tank has little room for surge.

Question 16: A driver of a tank vehicle on a slippery road must stop at an intersection ahead. Which approach reduces the risk caused by liquid surge?

Pump the brake pedal quickly several times
Wait to brake until the last moment so the liquid has less time to move
Brake early and gently, and leave extra room to stop (Correct answer)
Shift into neutral and let the liquid push the vehicle to a stop

Correct answer: Brake early and gently, and leave extra room to stop

Braking early and gently reduces the strength of the surge and gives more room to stop. Hard braking sends a large wave of liquid forward, which can push the vehicle into the intersection.

Question 17: Which tank design has no baffles or bulkheads inside and allows the most liquid surge?

Baffled tank
Smooth bore tank (Correct answer)
Bulkhead tank
Compartmented tank

Correct answer: Smooth bore tank

A smooth bore tank has nothing inside to slow the liquid, so surge is greatest. Its interior is also easy to clean.

Question 18: You are loading a tank that is only partly full. Which condition makes liquid surge most likely?

A tank filled completely with no air space
A smooth bore tank partly filled with liquid (Correct answer)
A tank with a low center of gravity
A tank divided into many small compartments

Correct answer: A smooth bore tank partly filled with liquid

A partly filled smooth bore tank has nothing to slow the liquid, so it can surge forward and back. Bulkheads and full tanks limit that movement.

Question 19: Which load condition requires a tank driver to be MOST concerned about liquid surge during braking?

A tank that is partially filled (Correct answer)
A tank with no liquid and no residue
A completely full tank
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.

Question 20: Before opening the dome of a tank that carries a flammable liquid for loading, what should you do about static electricity?

Wear rubber gloves only
Bond the tank to the fill pipe or grounded system before opening (Correct answer)
Run the engine to charge the battery
Spray the dome with water

Correct answer: Bond the tank to the fill pipe or grounded system before opening

Bonding the tank to the fill system equalizes the electrical charge so no spark jumps across the opening. Do this before opening the dome.

Question 21: Why does a tank that is completely full of liquid produce little surge when the truck brakes?

The tank walls absorb all of the braking force
Liquid becomes solid when the tank is full
Baffles are not needed in a full tank
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.

Question 22: 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 liquid foaming from vibration on rough roads
The pressure that builds in the tank as the liquid warms
The extra weight the tank carries when the liquid expands

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.

Question 23: Why must a tank driver leave room for outage when loading some liquids?

To make the tank easier to clean
To lower the vehicle's center of gravity
To reduce the amount of baffling required
To allow for liquid expansion as it warms (Correct answer)

Correct answer: To allow for liquid expansion as it warms

Liquids expand as they warm. Leaving outage, an empty space at the top, keeps the tank from overfilling or leaking.

Question 24: 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
Downshift to the lowest gear at high speed to stop the truck
Begin slowing well before the sign and brake gently throughout (Correct answer)

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.

Question 25: A baffled tank is partly full. Which statement about surge in it is correct?

Baffles stop side-to-side surge but not front-to-back surge
Baffles help control front-to-back surge, but side-to-side surge can still occur (Correct answer)
Baffles remove all surge, so side-to-side movement is no concern
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.

Question 26: How does a bulkhead differ from a baffle?

A bulkhead is an outer shell, while a baffle is an inner lining
A bulkhead divides the tank into separate compartments, while a baffle has holes that let liquid pass through (Correct answer)
A bulkhead is found only in smooth bore tanks, while a baffle is found only in compartment tanks
A bulkhead has holes to let liquid through, while a baffle seals compartments off completely

Correct answer: A bulkhead divides the tank into separate compartments, while a baffle has holes that let liquid pass through

Bulkheads divide a tank into separate compartments, and liquid cannot flow between them. Baffles have holes that let liquid pass through while slowing its movement.

Question 27: Which hazard is NOT removed by baffles in a baffled tank?

Front-to-back surge on a long downgrade
Side-to-side liquid surge that can contribute to rollover (Correct answer)
Liquid sloshing when the tank is nearly full
Any liquid movement at all

Correct answer: Side-to-side liquid surge that can contribute to rollover

Baffles help with front-to-back surge but give little protection against side-to-side movement. Liquid shifting sideways on a curve can still raise the risk of rollover.

Question 28: Product begins leaking from a hose connection while you are unloading a cargo tank. What should you do first?

Cover the spill with a tarp
Wait for the delivery to finish
Drive the truck away from the leak
Activate the emergency shutoff or stop the flow of product (Correct answer)

Correct answer: Activate the emergency shutoff or stop the flow of product

Stopping the flow, using the emergency shutoff if needed, limits the amount released. Driving away or waiting makes the spill worse.

Question 29: Why must a tank vehicle driver take a curve at a lower speed than a typical straight-body truck would?

Tank walls limit how far the steering wheel can turn
Tank vehicles have poor engine power in turns
The liquid's weight raises the center of gravity, which increases rollover risk (Correct answer)
Tires on tank vehicles have less grip than other truck tires

Correct answer: The liquid's weight raises the center of gravity, which increases rollover risk

Liquid cargo sits high and raises the vehicle's center of gravity, so a tank vehicle can roll over at speeds that would be safe for other trucks. Slow down before the curve.

Question 30: Which statement about tank vehicles and rollover risk is correct?

A tank vehicle's center of gravity is very low, so rollovers are rare
Baffles remove all danger of rollover
Liquid cargo gives a tank vehicle a high center of gravity, which raises rollover risk on curves (Correct answer)
Rollover risk is the same for a tank vehicle as for a flatbed carrying the same weight

Correct answer: Liquid cargo gives a tank vehicle a high center of gravity, which raises rollover risk on curves

Many tanks carry liquid high above the road, so the center of gravity is high. This makes rollovers more likely, especially on curves and ramps.

CDL Tank Vehicle (N) Endorsement Knowledge Test

The federal CDL knowledge test for drivers who haul liquids or gases in tank vehicles. It covers tank types and construction, baffled and unbaffled tanks, liquid surge, braking, handling on grades and curves, and emergency and regulatory requirements.

Questions

40 min

Time Limit

80%

To Pass

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These practice questions were written with AI tools. They are not real exam questions. Exam facts are checked against the official sources listed below. Not reviewed by a subject-matter expert. Editorial policy

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