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The air brakes endorsement applies to applicants who wish to drive a vehicle with air brakes in Class A, B, or C CDL. To drive a vehicle with air brakes, you must pass the air brake component of the Iowa CDL knowledge test. The IA CDL air brakes test consists of 25 questions, and you'll need at least 20 correct answers to pass (80%). The test covers the information found in the air brakes section of the Iowa CDL Manual. Take this IA CDL practice test now to prepare for the actual air brakes test!
1. With brake drums, if brakes become too hot:
the brakes may stop working.
your ABS will malfunction.
the brakes will supply too much power to the drive wheels.
2. The air storage tanks:
stop the compressor from pumping air.
are used to hold compressed air.
are connected to the engine through gears or a v-belt.
3. You are driving on a steep downgrade. If your safe speed is 35 mph, you should apply the brakes when your speed reaches:
35 mph
25 mph
30 mph
4. If air pressure does not build up fast enough:
you should turn the electrical power on and step on and off the brake pedal.
the pressure may drop too low during driving.
you should put the parking brake on and gently pull against it in a low gear.
5. Before driving a truck or bus with a dual air brake system, the minimum pressure in both the primary and secondary systems should be at least:
100 psi.
130 psi.
75 psi.
6. If your vehicle is equipped with air brakes, loss of air pressure in the emergency line causes:
the speed of your vehicle to increase.
the trailer emergency brakes to come on.
the trailer spring brakes to come on.
7. The safety valve is usually set to open at:
150 psi.
100 psi.
200 psi.
8. The air brake lag distance at 55 mph on dry pavement adds about:
32 feet.
75 feet.
60 feet.
9. When parking a trailer without spring brakes, it is very important for safety that you use wheel chocks. Why?
You may not notice a major leak in the service line until you try to put the brakes on.
if you don't use wheel chocks, supply air will be sent to the service line instead of going to charge the trailer air tanks.
The air could leak out of the trailer air tank, releasing its emergency brakes.
10. A broken exhaust system:
poses no threat to the driver.
can let poisonous carbon monoxide to leak into the cab.
can improve fuel efficiency.
 
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Frequently Asked Questions

If you are under 18, you must follow the Iowa Graduated Driver Licensing (GDL) Program. Here are the three phases of the program and the corresponding ages:

  1. Instruction permit? you must be 14 years old. After holding the permit for six months without traffic violation, you can also apply for a minor school license at 14 ½ years old. This special permit is optional and allows you to drive to school or to school activities within a 50-mile distance from your home.
  2. Intermediate license ? you must be 16 years old and have held an instruction permit for 12 months.
  3. Full license ? you must be at least 17 and have held an intermediate license for 12 months. Alternatively, you can directly obtain a class C driver's license at 18.
You have two options:

  1. You can schedule an appointment to take the exam at a service center. Simply locate the nearest Iowa DMV branch and choose your preferred date and time.
  2. If you are a minor between 14 and 17, you can take the knowledge test at a participating school/agency or at home using an electronic device connected to the internet. Once your parent completes and submits the application to Proctor Knowledge Exam Form, you’ll receive an email with instructions for proceeding. After successfully passing the exam, make an appointment to obtain the permit.

You can schedule an appointment for either option on the Iowa Department of Transportation website.

When applying for a driver’s license for the first time, you must bring the following documents:

  • Proof of identity, date of birth, and lawful status (e.g, U.S. passport, birth certificate, certificate of naturalization). If your legal name differs from your identity document, provide proof of the change, such as a certified marriage certificate, court order documents, or ID card.
  • Proof of Social Security Number (SSN).
  • Two proofs of Iowa residency and current residential address (e.g, Iowa voter registration card, utility bill, credit card statement…). If you are under 18 and unmarried, your parent/guardian must sign the Written Consent form to establish your residence. Additionally, provide a second printed document displaying your current name and current Iowa residential address, such as a report card or medical form.

You can use the online checklist provided by the Iowa DOT to ensure you have all the required documents. 

The DMV written test in Iowa is not exclusively provided in English but is offered in various languages, including Albanian, Arabic, Bosnian, Burmese, Cambodian, Chinese, French, German, Greek, Hebrew, Hmong, Italian, Korean, Laotian, Polish, Portuguese, Russian, Somali, Spanish, and Vietnamese. If you need an interpreter for a language not provided, you have to schedule an appointment.
To get ready for the DMV written test, start by reading the Iowa Driver License Manual. This manual has all the info you need to study for the exam: traffic signs, road rules, and safe driving practices. Then, check what you've learned with our free practice tests!

For new drivers in Iowa, various restrictions apply:

Instruction Permit
  • You cannot drive alone and you must be accompanied by a driver education instructor, a licensed parent/guardian, a licensed member of your family who is at least 21, or a licensed adult who is at least 25 (with parental permission if you are a minor).

Minor School License
  • You can't drive alone, except for school activities between 5 a.m. and 10 p.m.

Intermediate License
  • You cannot drive alone between 12:30 a.m. and 5 a.m., unless a parent/guardian completes a Waiver of Intermediate Driver’s License Hour Restriction form.
  • For the first six months, you cannot transport more than one minor without supervision, except for siblings.

The instruction permit is valid for four years. During this period, complete the 20 hours of supervised driving and after holding the permit for 12 months and maintaining a clean driving record for 6 months, you can apply for the intermediate license.
If you fail your DMV written test in Iowa, you have to wait at least one business day before retaking it. Before trying again, focus on the sections of the manual you have overlooked and consider signing up for DMV Premium to access additional practice tests!

IA CDL Air Brakes Test

Number of questions: 25
Correct answers to pass:20
Passing score:80%
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