Comprehensive Air Brake and
Vehicle Safety: CDL Practice Test
for Commercial Drivers.
Latest Updated Guide with 100%
Verified Answers,2026/2027
Edition.
What is true about antilock braking systems? - ansABS changes the way you brake in
emergencies.
When should parking brakes be used in air brake vehicles? - ansAnytime the vehicle is
parked.
What should you do if your antilock braking system is not working? - ansDrive normally, but
get the system serviced soon.
What can excessive use of the service brakes lead to? - ansExpansion of the brake drums.
What should you do if a low air pressure warning comes on for only one system? - ansStop
and safely park. Continue only after the system is fixed.
At what psi should the air compressor stop pumping? - ans130 psi.
What is the use of air brakes on a downgrade? - ansIt is only a supplement to the braking
effect of the engine.
How long should it take for air pressure to build from 85-100 psi? - ans45 seconds.
What can you do with dual parking control valves? - ansUse pressure from a separate tank to
release the spring emergency parking brakes to move a short distance.
What is the proper method of braking when going down long and/or steep grades? - ansBrake
until your speed is about 5 mph below your 'safe' speed, and then release your brakes.
What is the minimum thickness for brake drums or discs? - ans1/4 inch.
What does a supply pressure gauge tell you? - ansHow much pressure is in the air tanks.
Why does air braking take more time than hydraulic braking? - ansAir takes more time to
flow through the lines than hydraulic fluid.
What holds spring brakes back during normal driving? - ansAir pressure.
What may happen if you don't keep the alcohol evaporator filled? - ansIce may form in the air
storage tanks and cause the brakes to fail.
What is the service brake system? - ansThe system that applies and releases the brakes when
the driver uses the brake pedal.
What should you do to test air service brakes? - ansBrake firmly when slowly moving
forwards.
How do you know your brakes are fading? - ansYou have to push the brake pedal harder to
control speed on a downgrade.
What is the maximum leak rate for the air brake system of a straight truck or bus? - ans2 psi
per minute with the engine off and the brakes released.
What does the braking power of the spring brakes depend on? - ansThe service brakes being
in adjustment.
What should you do if one system of a dual air brake system is low on pressure? - ansEither
the front or rear brakes will not be fully operational.
What can legally hold the parking or emergency brakes of trucks and buses? - ansSpring
pressure.
,Comprehensive Air Brake and
Vehicle Safety: CDL Practice Test
for Commercial Drivers.
Latest Updated Guide with 100%
Verified Answers,2026/2027
Edition.
What are the three different systems combined in modern air brake systems? - ansService,
parking, and emergency brakes.
What does the air supply pressure gauge show? - ansHow much pressure is in the air tanks.
How should you brake in an emergency? - ansBrake so you can steer and your vehicle stays
in a straight line.
What should you do if your vehicle has an alcohol evaporator? - ansCheck and fill the alcohol
level every day during cold weather.
How much does the air brake lag distance add at 55 mph on dry pavement? - ans32 feet to
your stopping distance.
At what psi will the spring brakes on tractors and straight trucks bring your truck to a stop? -
ans20 psi.
What happens when you apply the brakes? - ansThe brake shoes/linings are pressed against
the brake drum.
What is the most important thing to do when a low air pressure warning comes on? - ansStop
and safely park as soon as possible.
What is the air loss rate for a straight truck or bus with the engine off and the brakes on? -
ansShould not be more than 3 psi in one minute.
What should you do to check that your service brakes are working properly? - ansWait for
normal air pressure, release the parking brake, move the truck forward slowly, and apply the
brake firmly.
What is the safety valve set to automatically reduce pressure at? - ans150 psi.
What is the effect of repeatedly pressing and releasing the brake pedal? - ansIt may result in
the loss of brake air pressure.
What should you do if spring brakes are on? - ansNever push the brake pedal.
What does the modulating control valve allow you to control? - ansThe spring brakes.
What may happen if you don't keep the unit filled with air? - ansIce may form in the air
storage tanks and cause the brakes to fail.
What does the S-cam do? - ansForces the brake shoes against the inside of the brake drum.
What is emergency stab braking? - ansBrake hard, release the brakes when the wheels lock,
and reapply the brakes when the wheels start rolling.
What can you use pressure from a separate tank for if your truck has dual parking control
valves? - ansRelease the spring emergency/parking brakes to move a short distance.
When is it not proper to apply the parking brakes? - ansWhen your brakes are very hot.
What does the application pressure gauge show? - ansHow much air pressure you are
applying to the brakes.
What happens if pressure does not build up fast enough? - ansYour air pressure may drop too
low during driving.
How much distance does the air brake lag add at 55 mph on dry pavement? - ans32 feet.
, Comprehensive Air Brake and
Vehicle Safety: CDL Practice Test
for Commercial Drivers.
Latest Updated Guide with 100%
Verified Answers,2026/2027
Edition.
What does the stop light switch do? - ansTurns on the brake lights to warn drivers behind
you.
Why should you drain water from compressed air tanks? - ansWater can freeze in cold
weather and cause brake failure.
What should you do when you reach your 'safe' speed of 40 mph on a steep downgrade? -
ansApply the service brakes until your speed drops to 35 mph.
What can hold the parking or emergency brake on a heavy vehicle? - ansSomething that
cannot leak, like spring pressure.
What can excessive heat in the brakes cause? - ansBrakes to fade or fail.
How should you check the brake slack on S-cam brakes? - ansPark on level ground, chock
the wheels, and release the parking brakes.
When should parking brakes be used with air brake vehicles? - ansWhenever you leave the
vehicle unattended.
What is the stopping distance required for a truck with air brakes going 55 mph? - ansMore
than 300 feet.
What can happen if you are cited for dumping or abandoning an animal on a highway? -
ansYou can be fined up to $1000 and jailed for six months.
What should you do when a school bus has stopped ahead and is flashing its red lights? -
ansStop as long as the red lights flash.
What should you not do when crossing double solid yellow lines? - ansPass other vehicles.
When stopped at railroad tracks with multiple tracks, when should you cross? - ansOnly
when you can see clearly in both directions.
When should you use your high-beam headlights at night? - ansWhenever it is legal and safe.
Where should you stop your vehicle if there is no crosswalk or limit line? - ansFifteen feet
before the corner.
What should you do to exit the freeway on the right from the lane closest to the center
divider? - ansChange lanes one at a time until you are in the proper lane.
What should you do at a flashing red traffic signal? - ansStop before entering, and then
proceed when safe.
When should you usually drive slower? - ansWhen you are near schools, playgrounds, and in
residential areas.
What must you notify the DMV within 5 days? - ansIf you sell or transfer your vehicle.
What should you do when backing out of an angled parking space? - ansAlways back slowly
and look over your right shoulder.
What is the usual speed limit in a business district unless otherwise posted? - ans25 mph.
What does a sign indicating parking is allowed mean? - ansOnly for disabled persons with a
special placard or plate.
Vehicle Safety: CDL Practice Test
for Commercial Drivers.
Latest Updated Guide with 100%
Verified Answers,2026/2027
Edition.
What is true about antilock braking systems? - ansABS changes the way you brake in
emergencies.
When should parking brakes be used in air brake vehicles? - ansAnytime the vehicle is
parked.
What should you do if your antilock braking system is not working? - ansDrive normally, but
get the system serviced soon.
What can excessive use of the service brakes lead to? - ansExpansion of the brake drums.
What should you do if a low air pressure warning comes on for only one system? - ansStop
and safely park. Continue only after the system is fixed.
At what psi should the air compressor stop pumping? - ans130 psi.
What is the use of air brakes on a downgrade? - ansIt is only a supplement to the braking
effect of the engine.
How long should it take for air pressure to build from 85-100 psi? - ans45 seconds.
What can you do with dual parking control valves? - ansUse pressure from a separate tank to
release the spring emergency parking brakes to move a short distance.
What is the proper method of braking when going down long and/or steep grades? - ansBrake
until your speed is about 5 mph below your 'safe' speed, and then release your brakes.
What is the minimum thickness for brake drums or discs? - ans1/4 inch.
What does a supply pressure gauge tell you? - ansHow much pressure is in the air tanks.
Why does air braking take more time than hydraulic braking? - ansAir takes more time to
flow through the lines than hydraulic fluid.
What holds spring brakes back during normal driving? - ansAir pressure.
What may happen if you don't keep the alcohol evaporator filled? - ansIce may form in the air
storage tanks and cause the brakes to fail.
What is the service brake system? - ansThe system that applies and releases the brakes when
the driver uses the brake pedal.
What should you do to test air service brakes? - ansBrake firmly when slowly moving
forwards.
How do you know your brakes are fading? - ansYou have to push the brake pedal harder to
control speed on a downgrade.
What is the maximum leak rate for the air brake system of a straight truck or bus? - ans2 psi
per minute with the engine off and the brakes released.
What does the braking power of the spring brakes depend on? - ansThe service brakes being
in adjustment.
What should you do if one system of a dual air brake system is low on pressure? - ansEither
the front or rear brakes will not be fully operational.
What can legally hold the parking or emergency brakes of trucks and buses? - ansSpring
pressure.
,Comprehensive Air Brake and
Vehicle Safety: CDL Practice Test
for Commercial Drivers.
Latest Updated Guide with 100%
Verified Answers,2026/2027
Edition.
What are the three different systems combined in modern air brake systems? - ansService,
parking, and emergency brakes.
What does the air supply pressure gauge show? - ansHow much pressure is in the air tanks.
How should you brake in an emergency? - ansBrake so you can steer and your vehicle stays
in a straight line.
What should you do if your vehicle has an alcohol evaporator? - ansCheck and fill the alcohol
level every day during cold weather.
How much does the air brake lag distance add at 55 mph on dry pavement? - ans32 feet to
your stopping distance.
At what psi will the spring brakes on tractors and straight trucks bring your truck to a stop? -
ans20 psi.
What happens when you apply the brakes? - ansThe brake shoes/linings are pressed against
the brake drum.
What is the most important thing to do when a low air pressure warning comes on? - ansStop
and safely park as soon as possible.
What is the air loss rate for a straight truck or bus with the engine off and the brakes on? -
ansShould not be more than 3 psi in one minute.
What should you do to check that your service brakes are working properly? - ansWait for
normal air pressure, release the parking brake, move the truck forward slowly, and apply the
brake firmly.
What is the safety valve set to automatically reduce pressure at? - ans150 psi.
What is the effect of repeatedly pressing and releasing the brake pedal? - ansIt may result in
the loss of brake air pressure.
What should you do if spring brakes are on? - ansNever push the brake pedal.
What does the modulating control valve allow you to control? - ansThe spring brakes.
What may happen if you don't keep the unit filled with air? - ansIce may form in the air
storage tanks and cause the brakes to fail.
What does the S-cam do? - ansForces the brake shoes against the inside of the brake drum.
What is emergency stab braking? - ansBrake hard, release the brakes when the wheels lock,
and reapply the brakes when the wheels start rolling.
What can you use pressure from a separate tank for if your truck has dual parking control
valves? - ansRelease the spring emergency/parking brakes to move a short distance.
When is it not proper to apply the parking brakes? - ansWhen your brakes are very hot.
What does the application pressure gauge show? - ansHow much air pressure you are
applying to the brakes.
What happens if pressure does not build up fast enough? - ansYour air pressure may drop too
low during driving.
How much distance does the air brake lag add at 55 mph on dry pavement? - ans32 feet.
, Comprehensive Air Brake and
Vehicle Safety: CDL Practice Test
for Commercial Drivers.
Latest Updated Guide with 100%
Verified Answers,2026/2027
Edition.
What does the stop light switch do? - ansTurns on the brake lights to warn drivers behind
you.
Why should you drain water from compressed air tanks? - ansWater can freeze in cold
weather and cause brake failure.
What should you do when you reach your 'safe' speed of 40 mph on a steep downgrade? -
ansApply the service brakes until your speed drops to 35 mph.
What can hold the parking or emergency brake on a heavy vehicle? - ansSomething that
cannot leak, like spring pressure.
What can excessive heat in the brakes cause? - ansBrakes to fade or fail.
How should you check the brake slack on S-cam brakes? - ansPark on level ground, chock
the wheels, and release the parking brakes.
When should parking brakes be used with air brake vehicles? - ansWhenever you leave the
vehicle unattended.
What is the stopping distance required for a truck with air brakes going 55 mph? - ansMore
than 300 feet.
What can happen if you are cited for dumping or abandoning an animal on a highway? -
ansYou can be fined up to $1000 and jailed for six months.
What should you do when a school bus has stopped ahead and is flashing its red lights? -
ansStop as long as the red lights flash.
What should you not do when crossing double solid yellow lines? - ansPass other vehicles.
When stopped at railroad tracks with multiple tracks, when should you cross? - ansOnly
when you can see clearly in both directions.
When should you use your high-beam headlights at night? - ansWhenever it is legal and safe.
Where should you stop your vehicle if there is no crosswalk or limit line? - ansFifteen feet
before the corner.
What should you do to exit the freeway on the right from the lane closest to the center
divider? - ansChange lanes one at a time until you are in the proper lane.
What should you do at a flashing red traffic signal? - ansStop before entering, and then
proceed when safe.
When should you usually drive slower? - ansWhen you are near schools, playgrounds, and in
residential areas.
What must you notify the DMV within 5 days? - ansIf you sell or transfer your vehicle.
What should you do when backing out of an angled parking space? - ansAlways back slowly
and look over your right shoulder.
What is the usual speed limit in a business district unless otherwise posted? - ans25 mph.
What does a sign indicating parking is allowed mean? - ansOnly for disabled persons with a
special placard or plate.
