CDL Greenlight

Free CDL practice test

5 questions, no signup. Miss one and see exactly why.

ANSWER KEY

All 5 questions, answered.

See each answer and why it’s right.

  1. General Knowledge

    You stop on a one-way or divided highway. Where do the warning devices go?
    1. 10 feet, 200 feet and 500 feet toward the approaching traffic
    2. 10 feet and 100 feet behind, and 100 feet ahead of the vehicle
    3. 50 feet, 100 feet and 500 feet toward the approaching traffic
    4. 10 feet, 100 feet and 200 feet toward the approaching trafficCorrect answer

    The rule

    1. On a one-way or divided highway, traffic approaches from one direction only.

    2. All three devices go on that side.

    3. They stand 10, 100 and 200 feet from the vehicle.

    Commercial driver manual, section 2.5place warning devices 10 feet, 100 feet, and 200 feet toward the approaching traffic.

    Why the other choices are wrong

    • No device goes out to 500 feet. That figure belongs to hills and curves: if drivers within 500 feet cannot see your vehicle, the rear-most triangle moves farther back. The set here is 10, 100 and 200 feet.

    • That is the pattern for a road with traffic in both directions, where one device warns the drivers coming toward your front. On a one-way or divided highway nobody comes from the front, so all three go behind you.

    • The first device stands 10 feet from the vehicle, not 50, and none goes out to 500 feet. The set is 10, 100 and 200 feet.

  2. General Knowledge

    With a lot of water on the road, what is the lowest speed at which hydroplaning can occur?
    1. 30 mphCorrect answer
    2. 50 mph
    3. 40 mph
    4. 60 mph

    The rule

    1. It does not take a lot of speed.

    2. With a lot of water, hydroplaning can start at 30 mph.

    3. It is more likely when tire pressure is low or the tread is worn.

    Commercial driver manual, section 2.6Hydroplaning can occur at speeds as low as 30 mph if there is a lot of water.

    Why the other choices are wrong

    • Too high. The tires can ride up on the water at only 30 mph, so slowing to 50 on a flooded road does not put you in the clear.

    • Still too high. With a lot of water, the manual puts the figure at 30 mph.

    • Hydroplaning is not only a highway-speed problem. With a lot of water it can start at half that speed, 30 mph.

  3. Air Brakes

    You have started a vehicle with a dual air system. The primary gauge shows 100 psi, but the secondary gauge shows only 70 psi. What should you do before driving?
    1. Drive off, because one system at 100 psi is enough for normal braking
    2. Drive off slowly, because the second system fills faster on the road
    3. Wait until the compressor has built up at least 100 psi in both systemsCorrect answer
    4. Wait only until the low air warning light and buzzer have shut off

    The rule

    1. Before driving, allow time for the air compressor to build up pressure.

    2. You need a minimum of 100 psi in both the primary and the secondary system.

    3. Watch both air pressure gauges, or both needles if the system has two needles in one gauge.

    Commercial driver manual, section 5.2Before driving a vehicle with a dual air system, allow time for the air compressor to build up a minimum of 100 psi pressure in both the primary and secondary systems.

    Why the other choices are wrong

    • A dual system is two separate brake systems, and the 100 psi minimum applies to both of them. A full primary system does not make up for a secondary system at 70 psi.

    • The pressure is built before you drive, not on the road. Give the compressor time until both systems show at least 100 psi.

    • The warning shuts off at a value the manufacturer sets, and that value only has to be greater than 55 psi. A quiet buzzer can still leave you well short of 100 psi in both systems.

  4. Combination Vehicles

    You are driving down the highway and need to slow your combination. Which brake control should you use?
    1. The foot brake, which sends air to all of the brakesCorrect answer
    2. The trailer hand valve, which brakes the trailer first
    3. The trailer air supply knob, which sets the emergency brakes
    4. The parking brake knob, which applies the spring brakes

    The rule

    1. The foot brake sends air to all of the brakes on the vehicle, including the trailers.

    2. There is much less danger of causing a skid or jackknife when you use just the foot brake.

    3. The trailer hand valve should be used only to test the trailer brakes.

    Commercial driver manual, section 6.2The foot brake sends air to all of the brakes on the vehicle (including the trailer(s)). There is much less danger of causing a skid or jackknife when using just the foot brake.

    Why the other choices are wrong

    • The hand valve works the trailer brakes alone, and braking the trailer by itself can make it skid. Use the hand valve only to test the trailer brakes.

    • Pulling the trailer air supply knob shuts off the trailer's air and puts on its emergency brakes. It is not a control for slowing down in traffic.

    • The parking brakes are for parking. To slow down on the road, use the one control that sends air to all of the brakes: the foot brake.

  5. Hazardous Materials

    You are driving with hazardous materials on board. Where should you keep the shipping papers?
    1. In the glove compartment, underneath the other papers for the trip
    2. In the sleeper berth, together with your other personal documents
    3. In the trailer, attached to the first package of the hazardous load
    4. In a pouch on the driver's door, or in clear view within reach with your seat belt onCorrect answer

    The rule

    1. While driving, the papers go in a pouch on the driver's door or in clear view within immediate reach with the seat belt fastened.

    2. Firefighters and police must be able to locate them quickly after a crash.

    3. When you are out of the vehicle, they go on the driver's seat or in the door pouch.

    Commercial driver manual, section 9.3In a pouch on the driver's door, or In clear view within immediate reach while the seat belt is fastened while driving, or On the driver's seat when out of the vehicle.

    Why the other choices are wrong

    • Under other papers is where nobody finds them. Hazardous materials papers go on top, in the door pouch or in clear view within reach.

    • The sleeper berth is not within immediate reach while your seat belt is fastened. Firefighters and police need to find the papers fast after a crash.

    • The trailer is not one of the allowed places. While you drive, the papers stay with you: in the door pouch, or in clear view within immediate reach.

ON THE REAL TEST

Which tests you take.

Each test needs at least 80 percent to pass.

General Knowledge
Everyone takes it.
Air Brakes
If your vehicle has air brakes.
Combination Vehicles
For a tractor-trailer.
Endorsements
One test each: Hazardous Materials, Tank Vehicles, Doubles and Triples, Passenger, School Bus.

This page is a 5-question sample. The course teaches all 8 tests, lesson by lesson. What’s inside