CDL Tank Tank Types and Construction — Questions and Answers
Question 1: For endorsement purposes, which description best fits a vehicle that needs a tank vehicle (N) endorsement?
- A vehicle hauling a tank of any size that holds liquid or gas
- A vehicle hauling a tank with an individual rated capacity over 119 gallons and an aggregate rated capacity of 1,000 gallons or more (Correct answer)
- A vehicle hauling only tanks that are permanently welded to the frame
- A vehicle hauling a tank that holds more than 500 gallons of any one liquid
Correct answer: A vehicle hauling a tank with an individual rated capacity over 119 gallons and an aggregate rated capacity of 1,000 gallons or more
Under federal rules, a tank vehicle carries liquid or gas in tanks with an individual rated capacity over 119 gallons and an aggregate rated capacity of 1,000 gallons or more. The tank may be permanently or temporarily attached.
The federal definition has two parts. Each tank must have an individual rated capacity of more than 119 gallons. The tanks together must have an aggregate rated capacity of 1,000 gallons or more. The tank can be permanently or temporarily attached to the vehicle or chassis, so a portable tank loaded onto a flatbed can still qualify. A driver who meets the definition needs the N endorsement. A driver who also hauls placarded hazardous materials needs the hazmat endorsement.
Question 2: A driver hauls several portable tanks on a flatbed. Each tank has a rated capacity of 100 gallons, and together they hold 1,200 gallons. Under the federal definition, is this a tank vehicle?
- Yes, because the aggregate capacity is 1,000 gallons or more
- Yes, because any portable tank on a flatbed counts as a tank vehicle
- No, because portable tanks are never counted
- No, because no individual tank is rated over 119 gallons (Correct answer)
Correct answer: No, because no individual tank is rated over 119 gallons
Both conditions must be met. Each tank must be rated over 119 gallons and the aggregate must be 1,000 gallons or more. Here the individual tanks are only 100 gallons.
The definition is a two-part test, and a vehicle must pass both parts. The aggregate here is 1,200 gallons, which clears the 1,000-gallon threshold. But each tank is rated at only 100 gallons, which does not exceed 119 gallons, so the individual-tank test fails. Portable tanks can count when they meet both tests, because the rule covers tanks temporarily attached to the vehicle. In this case, though, the vehicle does not meet the definition.
Question 3: What is the main purpose of baffles inside a tank?
- To keep different liquids in separate sections
- To make the tank easier to clean
- To slow the liquid's forward-and-back surge (Correct answer)
- To raise the load's center of gravity
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.
Baffles are partitions with openings that let liquid move through the tank. They help control forward-and-back surge when you speed up or brake. They do not stop side-to-side movement, which can still contribute to rollovers on curves. Bulkheads, which have no holes, are the walls that create separate compartments.
Question 4: How does a bulkhead differ from a baffle?
- A bulkhead divides the tank into separate compartments, while a baffle has holes that let liquid pass through (Correct answer)
- A bulkhead has holes to let liquid through, while a baffle seals compartments off completely
- A bulkhead is found only in smooth bore tanks, while a baffle is found only in compartment tanks
- A bulkhead is an outer shell, while a baffle is an inner lining
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.
A bulkhead is a solid wall, so each compartment behaves like its own small tank. Surge is limited to the liquid within a single compartment. A baffle has openings, so liquid still moves through the tank but its forward-and-back surge is slowed. Bulkheads also let a driver carry different products or divide the load. Baffles only control how the liquid moves.
Question 5: Which tank design has no baffles or bulkheads inside and allows the most liquid surge?
- Smooth bore tank (Correct answer)
- Baffled tank
- Compartmented tank
- Bulkhead 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.
Smooth bore tanks have no internal baffles or bulkheads. Liquid can move freely, so forward-and-back surge is the worst of any design. These tanks are common for food products such as milk because they are simple to clean. Drivers need to brake and accelerate very gently, especially with a partly filled tank. The forces from a surge can push the vehicle in ways that are hard to control.
Question 6: Why does a smooth bore tank call for especially gentle braking and acceleration?
- The tank walls flex under braking and can crack
- The liquid can surge freely from end to end, which can push the vehicle (Correct answer)
- The brakes on tank vehicles are weaker than on other trucks
- Smooth bore tanks cannot hold more than a half load
Correct answer: The liquid can surge freely from end to end, which can push the vehicle
With no internal barriers, the liquid moves freely and its momentum can push the truck forward or back.
A smooth bore tank has no baffles or bulkheads, so nothing restrains the liquid. When you brake, the liquid surges forward and can push the vehicle ahead. When you accelerate, it surges back. The effect is strongest in a tank that is only partly full. Smooth, early braking and gradual acceleration reduce the force of the surge.
Question 7: 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.
Outage is the empty space left at the top of a tank. Liquids expand when they are heated by the sun or by the product's own temperature. A tank filled to the brim could overflow or leak as the load warms. How much outage a load needs depends on how much the liquid expands. Liquids that expand more need more outage.
Question 8: Which statement about tank vehicles and rollover risk is correct?
- Rollover risk is the same for a tank vehicle as for a flatbed carrying the same weight
- Liquid cargo gives a tank vehicle a high center of gravity, which raises rollover risk on curves (Correct answer)
- A tank vehicle's center of gravity is very low, so rollovers are rare
- Baffles remove all danger of rollover
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.
Liquid in a tank is carried high, so the vehicle has a high center of gravity. This makes rollover more likely in turns, on ramps and in sudden lane changes. Liquid moving side to side can add to the problem. Baffles slow forward-and-back surge but do not eliminate the danger of side-to-side movement. Drivers should take curves and ramps well below the posted speed.
Question 9: A baffled tank still has what remaining surge concern?
- There is no surge at all in a baffled tank
- Surge is greater than in a smooth bore tank
- Liquid can still move side to side, which can contribute to a rollover (Correct answer)
- Surge occurs only when the tank is completely full
Correct answer: Liquid can still move side to side, which can contribute to a rollover
Baffles slow forward-and-back movement, but liquid can still move side to side. That sideways movement can contribute to rollovers.
Baffles are partitions with holes that help control forward-and-back surge. They do not stop liquid from shifting from side to side. That sideways movement can add to rollover risk on curves, so a baffled tank still calls for slower speeds in turns. Smooth bore tanks have no baffles at all and so have the greatest surge.
Question 10: A driver is loading a tank with several separate compartments. What is true of the surge in a bulkhead-divided tank?
- Surge is limited to the liquid within each compartment (Correct answer)
- Surge is the same as in a smooth bore tank of equal total size
- Surge cannot happen if every compartment is filled partially
- Surge in one compartment is passed to all the others through holes
Correct answer: Surge is limited to the liquid within each compartment
Bulkheads are solid, so each compartment acts as its own tank. Liquid can surge only within its own compartment.
Bulkheads divide a tank into separate sections with no openings between them. Each compartment behaves like a separate smaller tank. Liquid can surge only inside its own compartment, so the total surge is smaller than in one big open tank. Partly filled compartments can still surge, so smooth driving still matters. Filling each compartment completely, within weight limits and outage needs, reduces surge.
CDL Tank Tank Types and Construction
For endorsement purposes, which description best fits a vehicle that needs a tank vehicle (N) endorsement?
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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