How many questions are on the South Dakota CDL knowledge test?

The South Dakota CDL general knowledge test has 50 multiple-choice questions, and you need 80% (40 correct) to pass. Each endorsement test like Air Brakes is shorter (typically 20-30 questions) but uses the same 80% threshold.

What's the minimum age for a CDL in South Dakota?

In South Dakota, the minimum age for a CDL is 18 (intrastate); 21 (interstate). Federal law requires drivers to be 21+ to drive a CMV across state lines or to transport hazardous materials, regardless of state minimum age.

Is air brakes a separate endorsement or a restriction removal?

Air brakes is technically a restriction removal rather than an endorsement. If you do not pass the air brakes test, your CDL will carry a restriction code (typically 'L' or 'Z') that limits you to vehicles without air brakes or with only an air-over-hydraulic system. Passing the test removes this restriction.

Do I need to take both a written and skills test for air brakes?

Yes. You must pass the air brakes knowledge test (written/computer) and demonstrate air brake proficiency during the CDL skills test. The skills test includes a pre-trip air brake inspection where you must identify components and perform pressure tests. If you take your road test in a vehicle with air brakes, both are covered.

What is brake lag and why is it important for the test?

Brake lag is the time delay between pressing the brake pedal and the brakes actually engaging. In air brake systems, this delay is about 0.4 seconds because air must travel through the lines to reach the brake chambers. This adds roughly 32 feet of travel distance at 55 mph compared to hydraulic brakes. The test frequently asks about this concept.

What PSI numbers do I need to memorize for the air brakes test?

Key numbers include: the governor cut-out pressure (around 125 PSI), cut-in pressure (around 100 PSI), low-pressure warning activation (60 PSI), emergency spring brake engagement (20-45 PSI), and the maximum air pressure loss rates during the static and applied leak tests (2 PSI per minute for single vehicles, 3 PSI for combinations).

Can I get a CDL without the air brakes qualification?

Yes, but your CDL will carry an air brake restriction, severely limiting the vehicles you can drive. Most tractor-trailers, buses, and large trucks use air brakes, so the restriction effectively excludes you from the majority of CDL jobs. Most CDL training programs include air brake training as standard.

South Dakota CDL air brakes practice test

Updated for 2026 · 35 air brakes questions of 442 across the full SD CDL path · Aligned to the commercial driver manual · Part of the SD CDL path

Start with general knowledge first. We recommend completing it before drilling air brakes questions.

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Removes the air brake restriction. Required for most heavy trucks and buses.

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2 tests, each drawing from a different question pool. Take all 2 to cover the full 35 questions.

Quick test

15 random questions from the air brakes pool. Try it free.

15 questions80% to pass

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35 questions covering the full air brakes bank. Take when you're ready for everything.

35 questions80% to pass

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Drill 35 Air Brakes Questions

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Drill every question in this section with full explanations.

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About the South Dakota Air Brakes test

The air brakes knowledge test typically has 25 multiple-choice questions, and you need at least 80% to pass. Questions cover the components of an air brake system (compressor, governor, reservoirs, brake chambers, slack adjusters), how to inspect air brakes, the proper procedure for testing low-pressure warning devices, the brake lag distance unique to air brakes, and emergency and parking brake systems. You will also be tested on the air brake inspection portion of the CDL pre-trip test. In South Dakota, this test is administered by the DPS as part of the standard CDL knowledge exam - review the South Dakota CDL manual section on air brakes for the most accurate state-specific content.