Take CDL Commercial Driver's License Knowledge Test

QUESTION 1 / 25

What is the purpose of the air compressor in an air brake system?

Choose one answer below.

ATo cool the brakes✓BTo pump air into storage tanks to provide the energy for braking✓CTo inflate the tires✓DTo power the horn✓

QUESTION 2 / 25

At what PSI should the low air pressure warning activate?

Choose one answer below.

A40 PSI✓B60 PSI✓C80 PSI✓D100 PSI✓

QUESTION 3 / 25

What happens when the air pressure drops too low in the brake system?

Choose one answer below.

AThe brakes release completely✓BThe spring brakes automatically apply, bringing the vehicle to a stop✓CThe engine shuts off✓DNothing, the brakes work the same✓

QUESTION 4 / 25

What is the purpose of the air brake system's governor?

Choose one answer below.

ATo control the speed of the vehicle✓BTo control the air compressor by starting it when pressure drops and stopping it when pressure reaches the maximum✓CTo regulate brake pedal pressure✓DTo measure tire pressure✓

QUESTION 5 / 25

What is 'brake lag' in air brake systems?

Choose one answer below.

AA braking defect✓BThe delay between pressing the brake pedal and the brakes actually applying, typically about 0.5 seconds✓CThe sound brakes make when applied✓DThe distance traveled while braking✓

QUESTION 6 / 25

What is the air brake cut-in and cut-out pressure range?

Choose one answer below.

A50-75 PSI✓B80-100 PSI✓C100-125 PSI✓D125-150 PSI✓

QUESTION 7 / 25

What is the primary purpose of properly securing cargo?

Choose one answer below.

ATo make the truck look neat✓BTo prevent cargo from shifting or falling, which could cause accidents or damage✓CTo reduce fuel consumption✓DTo make loading easier next time✓

QUESTION 8 / 25

According to FMCSA regulations, how often must cargo be inspected during a trip?

Choose one answer below.

AOnly before the trip starts✓BWithin the first 50 miles and every 150 miles or 3 hours thereafter✓COnce per day✓DOnly if the driver suspects a problem✓

QUESTION 9 / 25

What is the purpose of blocking and bracing cargo?

Choose one answer below.

ATo increase the vehicle weight✓BTo prevent forward, backward, and lateral movement of cargo during transport✓CTo make unloading easier✓DTo protect the trailer floor✓

QUESTION 10 / 25

What type of tie-down is most appropriate for securing heavy machinery on a flatbed?

Choose one answer below.

ABungee cords✓BChains with binders rated for the weight of the load✓CRope✓DShrink wrap✓

QUESTION 11 / 25

What is the aggregate working load limit for cargo securement?

Choose one answer below.

AEqual to the weight of the cargo✓BAt least 50% of the cargo weight for all tie-downs combined✓C25% of the cargo weight✓DAny amount is sufficient✓

QUESTION 12 / 25

Where should the heaviest cargo be placed in a trailer?

Choose one answer below.

AAt the rear for easy unloading✓BLow and centered over the axles for optimal weight distribution and stability✓CAt the front near the cab✓DIt does not matter where heavy items go✓

QUESTION 13 / 25

What is the primary danger of trailer swing (trailer jackknife)?

Choose one answer below.

AThe trailer overheats✓BThe trailer swings out and may strike other vehicles or cause a rollover✓CThe engine stalls✓DThe landing gear collapses✓

QUESTION 14 / 25

When coupling a tractor to a semi-trailer, what must you verify about the fifth wheel?

Choose one answer below.

AThe fifth wheel is dry and ungreased✓BThe kingpin is locked in the fifth wheel jaws and the locking lever is secured✓CThe fifth wheel plate is exactly level with the trailer floor✓DThe trailer air lines are connected before coupling✓

QUESTION 15 / 25

What is the correct procedure for testing trailer brakes after coupling?

Choose one answer below.

AApply service brakes at highway speed and note stopping distance✓BWith tractor and trailer connected, move forward slowly while applying only the trailer hand valve✓CApply the parking brake only and release it quickly✓DHave a passenger watch the trailer wheels while you drive past✓

QUESTION 16 / 25

When uncoupling a semi-trailer, what must you do before cranking the landing gear down?

Choose one answer below.

ADisconnect the air lines first✓BLower the trailer on a firm, level surface and apply the trailer parking brake✓CRemove the kingpin safety lock✓DDrain the air tanks completely✓

QUESTION 17 / 25

Which air line on a combination vehicle supplies continuous air to the trailer to charge the emergency brakes?

Choose one answer below.

AService line (blue)✓BEmergency line (red)✓CAuxiliary supply line (green)✓DControl line (yellow)✓

QUESTION 18 / 25

What is rearward amplification in a doubles or triples combination?

Choose one answer below.

AThe tendency of the rear trailer to whip more violently than the front during swerving✓BThe increase in engine noise at higher speeds✓CThe amplified braking force at the rear axle✓DThe magnified turn radius of a long combination✓

QUESTION 19 / 25

What is the minimum age to obtain a Commercial Driver's License (CDL) for interstate driving in the United States?

Choose one answer below.

A18 years old✓B19 years old✓C21 years old✓D25 years old✓

QUESTION 20 / 25

What are the three classes of CDL?

Choose one answer below.

AClass 1, 2, and 3✓BClass A, B, and C✓CClass X, Y, and Z✓DClass I, II, and III✓

QUESTION 21 / 25

What is the maximum number of hours a commercial driver can drive after 10 consecutive hours off duty?

Choose one answer below.

A8 hours✓B10 hours✓C11 hours✓D14 hours✓

QUESTION 22 / 25

What is the GVWR?

Choose one answer below.

AGeneral Vehicle Registration Weight✓BGross Vehicle Weight Rating — the maximum safe weight of a vehicle including cargo✓CGovernment Vehicle Weight Restriction✓DGross Volume and Weight Report✓

QUESTION 23 / 25

What does the pre-trip inspection help prevent?

Choose one answer below.

ATraffic tickets✓BMechanical failures, accidents, and violations during operation✓CFuel waste only✓DParking difficulties✓

QUESTION 24 / 25

What is a CDL endorsement?

Choose one answer below.

AA signature on the license✓BAn additional qualification added to a CDL allowing the driver to operate specific vehicle types or carry certain cargo✓CA grade on the driving test✓DA recommendation from an employer✓

QUESTION 25 / 25

What is hydroplaning and at what speed does it typically begin?

Choose one answer below.

ADriving in a plane during rain✓BWhen tires ride on a layer of water rather than the road surface, typically starting around 30 mph on wet roads✓CDriving too slowly in rain✓DOnly happens at speeds above 70 mph✓