16 Tanker Endorsement (N) Practice Questions & Answers
Every Tanker Endorsement (N) practice question from the CDL Practice Test, with the correct answer and a short explanation.
Start practice test →1. What is 'liquid surge' and why does it matter when driving a tank vehicle?
- A.The vibration of the tank shell caused by uneven road surfaces
- B.The foaming of liquid caused by high temperatures inside the tank
- C.The movement of liquid in a partially filled tank, which can push the vehicle in the direction the liquid moves✓ Answer
- D.The pressure buildup that occurs when a tank is loaded completely full
Liquid surge is the wave of liquid moving back and forth in a partially filled tank. When you slow or stop, the liquid surges forward and can push the vehicle in the direction it is moving (for example, out into an intersection), so drivers must anticipate this force.
Source: FMCSA/AAMVA CDL Manual, Section 8.1.1 (Liquid Surge)Report a problem with this question
2. Why are tanks that carry liquids usually NOT loaded completely full?
- A.Because a full tank is impossible to legally weigh at a scale
- B.Because liquid cannot be pumped out of a completely full tank
- C.Because liquids expand as they warm, and space (outage) must be left for the liquid to expand✓ Answer
- D.Because full tanks always exceed the federal gross weight limit
You must not load a liquid tank completely full because liquids expand as they warm. The empty space left for expansion is called outage; different liquids expand by different amounts and need different amounts of outage.
Source: FMCSA/AAMVA CDL Manual, Section 8.1.3 (Outage)Report a problem with this question
3. How does a smooth-bore (unbaffled) tank differ from a baffled tank in terms of liquid surge?
- A.A smooth-bore tank has nothing inside to slow the liquid, so surge is much stronger than in a baffled tank✓ Answer
- B.There is no difference; both tank types produce identical surge
- C.A baffled tank has no internal divisions and therefore surges the most
- D.A smooth-bore tank has more internal walls, so it controls surge better than a baffled tank
Smooth-bore tanks have no baffles inside, so nothing slows the liquid's front-to-back movement; surge is very strong. Baffled tanks have bulkheads with holes that let liquid flow through while dampening the surge.
Source: FMCSA/AAMVA CDL Manual, Section 8.1.2 (Baffled Tanks / Smooth Bore Tanks)Report a problem with this question
4. What is the purpose of baffles inside a tank vehicle?
- A.They completely separate the tank into fully sealed, watertight compartments
- B.They are bulkheads with holes that control forward-and-back liquid surge✓ Answer
- C.They increase the tank's capacity by removing empty air space
- D.They control side-to-side surge to prevent the tank from tipping over
Baffles are bulkheads with holes that let liquid flow through them. They help control the forward-and-back surge, but they do NOT reduce side-to-side surge, which is why baffled tanks can still roll over in turns.
Source: FMCSA/AAMVA CDL Manual, Section 8.1.2 (Baffled Tanks)Report a problem with this question
5. What are bulkheads used for in a tank that has separate cargo compartments?
- A.They divide the tank into separate compartments, and loads must be balanced across them✓ Answer
- B.They automatically vent expanding vapor out of the tank
- C.They are holes that let liquid surge move freely between compartments
- D.They are external supports that raise the tank's center of gravity
Bulkheads divide a tank into separate liquid-tight compartments. When loading and unloading, you must keep the load balanced: too much weight on the front or rear axles, or too much on one side, makes the vehicle harder to control.
Source: FMCSA/AAMVA CDL Manual, Section 8.2.1 (How Much to Load / Bulkheads)Report a problem with this question
6. Why do tank vehicles have a high risk of rollover compared to other trucks?
- A.Tank vehicles have no brakes on the trailer axles
- B.A liquid load raises the center of gravity, making the vehicle top-heavy and easy to tip in turns✓ Answer
- C.The liquid load keeps the center of gravity very low, making them unstable
- D.Tank trailers are always lighter than the tractor pulling them
The liquid load raises the vehicle's center of gravity because the weight is high in the tank shell. A high center of gravity makes the vehicle top-heavy and easy to roll over, so tank drivers must go slowly around curves and turns.
Source: FMCSA/AAMVA CDL Manual, Section 8.1.4 (High Center of Gravity)Report a problem with this question
7. What is the correct way to take curves and on/off ramps in a tank vehicle?
- A.Slow down well below the posted speed limit before entering the curve✓ Answer
- B.Maintain the posted highway speed since the ramp speed signs are only advisory
- C.Speed up entering the curve to keep the liquid pressed against the back
- D.Brake hard in the middle of the curve to control surge
Because of the high center of gravity and liquid surge, you should slow down before a curve and stay well below the posted speed limit for turns and ramps. Posted ramp speeds are meant for cars, not top-heavy tank vehicles.
Source: FMCSA/AAMVA CDL Manual, Section 8.2.2 (Drive Smoothly / Curves)Report a problem with this question
8. What is the best braking technique to keep control of a tank vehicle and avoid skidding?
- A.Pump the brakes rapidly on and off during every stop
- B.Use only the trailer hand valve to slow the vehicle
- C.Wait until the last moment and brake hard to stop as quickly as possible
- D.Brake early and gently, allowing extra following distance and stopping space✓ Answer
You should brake early and gently and increase your following distance, because a tank vehicle's high center of gravity and liquid surge make it easy to skid or roll. Sudden, hard braking can cause the liquid to surge and the vehicle to lose control.
Source: FMCSA/AAMVA CDL Manual, Section 8.2.2 (Braking / Controlling Surge)Report a problem with this question
9. If a tank vehicle starts to skid, why is it especially dangerous to make sudden steering or braking movements?
- A.The tank will immediately vent its cargo if the steering wheel is turned quickly
- B.Hard braking is safe because tank vehicles cannot jackknife
- C.Sudden movements combined with liquid surge can throw the vehicle out of control and cause a rollover✓ Answer
- D.Sudden movements have no effect because the liquid keeps the vehicle stable
Steer and brake smoothly, because the liquid surge in a tank magnifies any sudden movement. Combined with the high center of gravity, an abrupt steering or braking input can push the vehicle past its balance point and cause a rollover or loss of control.
Source: FMCSA/AAMVA CDL Manual, Section 8.2.2 (Steer Gently / Controlling Surge)Report a problem with this question
10. You are hauling a partly loaded smooth-bore tank and must make a normal stop at an intersection. What should you expect?
- A.The liquid will hold the vehicle perfectly still with no surge at all
- B.The liquid will surge forward and back, so allow extra stopping distance and stop farther from the intersection✓ Answer
- C.The tank will pull sharply to the right every time you brake
- D.The vehicle will stop shorter than usual because the liquid adds braking force
In a smooth-bore tank there are no baffles, so front-to-back surge is very strong. When you stop, the surging liquid can keep pushing the vehicle forward, so you must leave extra stopping distance and stop back from intersections.
Source: FMCSA/AAMVA CDL Manual, Section 8.1.2 (Smooth Bore Tanks) and 8.2.2Report a problem with this question
11. Besides the normal vehicle inspection, what is important to check when inspecting a tank vehicle?
- A.The radio and air conditioning, which are critical to tank safety
- B.The tank body/shell for leaks and the vents, valves, hoses, and manhole covers✓ Answer
- C.Only the tire tread depth, ignoring the tank fittings
- D.Only the engine oil level, since tanks have no unique parts to inspect
When inspecting a tank vehicle you must check items unique to tanks: the tank body and shell for leaks, and the vents, valves, hoses, connections, and manhole covers. Leaking cargo or a clogged vent can be extremely dangerous.
Source: FMCSA/AAMVA CDL Manual, Section 8.2.3 (Inspecting Tank Vehicles)Report a problem with this question
12. Why must the vents (breather valves) on a tank be kept clear and working during inspection?
- A.Vents only matter on dry-bulk tanks, not liquid tanks
- B.Vents must be sealed shut to keep the liquid from expanding
- C.Clogged vents make the vehicle accelerate faster than normal
- D.If vents are clogged, pressure or vacuum can build up and damage the tank or cause it to collapse✓ Answer
Tank vents must work properly so air can move in and out as the tank is filled, emptied, or the liquid expands. If a vent is clogged, pressure or vacuum can build inside the tank and damage it, so vents must be checked and kept clear.
Source: FMCSA/AAMVA CDL Manual, Section 8.2.3 (Inspecting Tank Vehicles / Vents)Report a problem with this question
13. A baffled tank helps with one kind of surge but not another. Which statement is correct?
- A.Baffles eliminate all surge in every direction
- B.Baffles reduce forward-and-back surge but do not control side-to-side surge✓ Answer
- C.Baffles have no effect on surge in any direction
- D.Baffles reduce side-to-side surge but do not control forward-and-back surge
Baffles have holes that let liquid pass through, which dampens the forward-and-back surge. However, they do nothing to reduce side-to-side surge, so a baffled tank can still roll over when turning or changing lanes too fast.
Source: FMCSA/AAMVA CDL Manual, Section 8.1.2 (Baffled Tanks / Side-to-Side Surge)Report a problem with this question
14. Under federal rules, a tank vehicle endorsement (N) is required to drive a vehicle designed to haul liquids or gases in a tank whose individual rated capacity is more than 119 gallons AND whose aggregate rated capacity is at least how much?
- A.2,000 gallons or more
- B.119 gallons or more
- C.1,000 gallons or more✓ Answer
- D.500 gallons or more
The federal definition of a tank vehicle covers a tank with an individual rated capacity of more than 119 gallons AND an aggregate rated capacity of 1,000 gallons or more; both thresholds must be met, so this is the aggregate figure that triggers the N endorsement requirement.
Source: 49 CFR 383.5 (definition of tank vehicle)Report a problem with this question
15. A baffled cargo tank has bulkheads with holes that let liquid flow through them. Which type of liquid surge do these baffles help control?
- A.Only vertical bouncing from bumps
- B.Side-to-side surge
- C.All surge directions equally
- D.Forward-and-back surge✓ Answer
Baffles slow the forward-and-back movement of the liquid but do nothing to control side-to-side surge; that is why baffled tankers can still roll over on curves and ramps, and drivers must slow down well below posted speeds.
Source: AAMVA CDL Manual, Section 6 (Tank Vehicles) — Baffled TanksReport a problem with this question
16. When loading a liquid cargo tank, you must leave some empty space called "outage" rather than filling the tank completely. What is the reason for outage?
- A.Liquids expand as they warm up, so room is needed for expansion✓ Answer
- B.A completely full tank is illegal on every highway
- C.Empty space lowers the vehicle's center of gravity
- D.Liquids contract and shrink as they warm up
Liquids increase in volume as their temperature rises, so you must leave outage room for that expansion; the amount of outage needed varies because different liquids expand by different amounts.
Source: AAMVA CDL Manual, Section 6 (Tank Vehicles) — OutageReport a problem with this question
Practice questions based on the AAMVA/FMCSA model CDL manual. Requirements vary by state — study your state's official CDL manual before your exam. Official CDL info →