If a vehicle has anti-lock brakes on just one axle, the driver will still have more control during braking than they would without any anti-lock brakes.

Will provide increased control in braking.

Will not make a difference in braking.

Will provide increased control in braking.

Will likely cause the air brakes to malfunction.

You should test the tractor protection valve by allowing the air supply to properly charge, turning off the engine, then releasing air from the system by pressing the brake pedal several times. The tractor protection valve should move into its emergency position when psi drops to an unsafe level.

Releasing air with the brake pedal.

Pulling the yellow, diamond-shaped knob.

Releasing air with the brake pedal.

The trailer hand valve (also referred to as the "trolley valve" or "Johnson bar") works the trailer brakes and should be used only when testing them. Using the trailer hand valve while driving could result in a skid.

To check the connection between the trailer and tractor.

Older trailers do not have spring brakes. This means that if the air supply in an older trailer's air tank has leaked away, there will be no working brakes connected to the trailer and its wheels will turn freely.

The trailer will not have brakes.

The trailer will stop normally.

The trailer will not have brakes.

The emergency air line controls the emergency brakes on a combination vehicle. A loss of air pressure in the emergency line will cause the emergency trailer brakes to activate.

The emergency brakes will activate.

The Anti-Lock Braking System will activate.

The service air line will activate.

The emergency brakes will activate.

Combination Vehicles Practice Test | Iowa 2024 #1 Page 3 of 3

Train for FREE online with our Iowa CDL combination vehicle test. The official exam test consists of several obligatory parts, with all of them checking your knowledge of different blocks of road rules. If you need to obtain a IA combination license in 2024, practice as much as possible. Free sample tests published on our website will help you check and improve your knowledge and boost your grades. Please bear in mind that DMV requirements for issuing a combination license may vary from state to state.

Number of Question 20

Passing Score 16

Number of Tests 20

Combination Vehicles Practice Test | Iowa 2024 #1 Page 3 of 3

15 . Having anti-lock brakes on only one axle:

16 . A driver should test the tractor protection valve by:

17 . A trailer that is too high:

18 . The trailer hand valve should be used:

19 . Older trailers are not equipped with spring brakes. This means that if the air supply for a vehicle's air braking system leaks away:

20 . If the emergency air line loses pressure:

See the exact questions that will be on the 2024 DMV exam.

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