41 questions · General Knowledge + Endorsements · Free
41 practice questions for the Texas CDL knowledge test, written from Sections 2 through 10 of the Texas Commercial Motor Vehicle Drivers Handbook: driving safely, cargo, passengers, air brakes, combination vehicles, doubles and triples, tank vehicles, hazardous materials, and school buses. Every answer comes with a plain English explanation, a note on why each wrong choice fails, and the handbook page it comes from. Free, no account required.
This is practice for the Texas CDL knowledge test. Every question is based on Sections 2 through 10 of the Texas Commercial Motor Vehicle Drivers Handbook (DL-7C (Revised March 2026)), and each explanation cites the page it comes from. These are nine sections of the commercial handbook, so keep studying the Texas permit practice test and the rest of the commercial handbook alongside it.
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The questions here are practice, not the official test, and they cover Sections 2 through 10 of the handbook: general driving safety, cargo, passengers, air brakes, combination vehicles, doubles and triples, tank vehicles, hazardous materials, and school buses. Check the Texas licensing agency before your appointment for the current test format and fees.
Source: Texas Commercial Motor Vehicle Drivers Handbook (DL-7C (Revised March 2026), Texas Department of Public Safety). Downloaded and checked 2026-10-15.
Every question below comes from the Texas CDL question bank on this page. Open a question to see the correct answer and the explanation. Nothing here is hidden behind a signup.
1. Air brakes are really how many different braking systems combined?
Three: service, parking, and emergency. An air brake system looks like one pedal and one set of tanks, but it does three distinct jobs. The service brake system applies and releases the brakes when you use the brake pedal during normal driving. The parking brake system applies and releases the parking brakes when you use the parking brake control. The emergency brake system uses parts of the service and parking brake systems to stop the vehicle in a brake system failure. Knowing which system you are touching explains most of the controls in the cab.
2. What does an alcohol evaporator do in an air brake system?
It puts alcohol into the air system to reduce the risk of ice in valves and other parts during cold weather. Cold weather turns tank water into a brake failure, and the evaporator fights it chemically. Some air brake systems have an alcohol evaporator to put alcohol into the air system, which helps reduce the risk of ice in air brake valves and other parts during cold weather, because ice inside the system can make the brakes stop working. Check the alcohol container and fill up as necessary, every day during cold weather. It does not replace drainage: daily air tank drainage is still needed to get rid of water and oil unless the system has automatic drain valves.
3. What does the application pressure gauge tell you, and what does rising application pressure at the same speed mean?
How much air pressure you are applying to the brakes; needing more pressure to hold the same speed means the brakes are fading. The application gauge is a fade detector. It shows how much air pressure you are applying to the brakes, and increasing application pressure to hold the same speed means the brakes are fading, so you should slow down and use a lower gear. The need for increased pressure can also be caused by brakes out of adjustment, air leaks, or mechanical problems. Not all vehicles have this gauge, but drivers who do have an early-warning instrument most drivers lack.
4. What do the ABS dates require, and how can you tell a towed unit has ABS if it predates the requirement?
Truck tractors from March 1, 1997, other air brake vehicles from March 1, 1998; on older towed units, look underneath for the ECU and wheel speed sensor wires at the brakes. ABS fitment follows two March deadlines. Truck tractors with air brakes built on or after March 1, 1997, and other air brake vehicles, trucks, buses, trailers, and converter dollies, built on or after March 1, 1998, are required to be equipped with antilock brakes. Many older vehicles have ABS voluntarily. In the case of towed units manufactured before it was required by the Department of Transportation, it may be difficult to tell if the unit is equipped, so look under the vehicle for the electronic control unit and wheel speed sensor wires coming from the back of the brakes.
5. What are the maximum air leakage rates with a fully charged system, engine off and parking brake released?
Less than 2 psi in 1 minute for single vehicles and less than 3 psi in 1 minute for combination vehicles. Leakage is timed, not eyeballed. With a fully charged air system, typically 125 psi, turn off the engine, release the parking brake, and time the air pressure drop: the loss rate should be less than two psi in one minute for single vehicles and less than three psi in one minute for combination vehicles. Then, with pressure at governor cutoff, fully apply the foot brake for one minute and watch for drops of more than three pounds single or four pounds combination. If the loss rate is too much, check for leaks and fix them before driving, or you could lose your brakes on the road.
6. What is brake lag, and how much distance does it add at 55 mph on dry pavement?
The time required for the brakes to work after the pedal is pushed, as air flows through the lines; about 32 feet at 55 mph. Air brakes add a fourth term to stopping distance. With hydraulic brakes the brakes work instantly, but with air brakes it takes a little time, one half second or more, for the air to flow through the lines to the brakes; that delay is brake lag. Total stopping distance becomes perception plus reaction plus brake lag plus braking distance. The air brake lag distance at 55 mph on dry pavement adds about 32 feet, so the total for an average driver under good conditions is over 450 feet.
7. What do supply pressure gauges tell you, and what changes on a dual system?
How much pressure is in the air tanks; a dual system has a gauge for each half of the system, or a single gauge with two needles. Supply gauges are the fuel gauges of the air system. All vehicles with air brakes have a pressure gauge connected to the air tank, and these gauges tell you how much pressure is in the air tanks. If the vehicle has a dual air brake system, there will be a gauge for each half of the system, or a single gauge with two needles. Reading both halves is how you catch one system quietly dying while the other still looks fine.
8. What limits apply to brake drum cracks and lining condition at inspection?
Brake drums or discs must not have cracks longer than one half the width of the friction area, and linings must not be loose, soaked with oil or grease, or dangerously thin. Foundation brake hardware has measurable reject limits. Brake drums (or discs) must not have cracks longer than one half the width of the friction area; linings, the friction material, must not be loose or soaked with oil or grease, and they must not be dangerously thin. Mechanical parts must be in place, not broken or missing, and the air hoses connected to the brake chambers must not be cut or worn due to rubbing. These checks sit in Step 5 of the walk-around, next to the slack adjuster pull test.
9. How do you test the low air pressure warning signal?
Shut the engine off with enough pressure that the signal is not on, turn electrical power on, and step on and off the brake pedal to reduce tank pressure; the warning must come on before pressure drops below 55 psi in the lowest tank. The warning test manufactures low pressure safely, parked. Shut the engine off when you have enough air pressure so that the low pressure warning signal is not on, turn the electrical power on, and step on and off the brake pedal to reduce air tank pressure. The low air pressure warning signal must come on before the pressure drops to less than 55 psi in the air tank, or the tank with the lowest pressure in dual systems. If the signal does not work, you could lose air pressure without knowing it, facing sudden emergency braking or increased stopping distance with only limited braking before the spring brakes come on.
10. What should the air storage tanks be able to do if the compressor stops working?
Hold enough air to allow the brakes to be used several times, even if the compressor stops working. Tank capacity is your reserve after a compressor failure. Air storage tanks are used to hold compressed air, and the number and size of air tanks varies among vehicles. The tanks will hold enough air to allow the brakes to be used several times, even if the compressor stops working. Several times is not unlimited times: each application spends reserve that nothing replenishes, which is why a dead compressor means a prompt, planned stop rather than continued driving on stored air.
11. If one air system in a dual system is very low on pressure, what happens and what should you do?
Either the front or the rear brakes will not be operating fully, so it will take longer to stop; bring the vehicle to a safe stop and have the air brake system fixed. Half a brake system is a longer stop, not a minor note. The warning light and buzzer should come on before the air pressure drops below 55 psi in either system, and if this happens while driving, you should stop right away and safely park the vehicle. If one air system is very low on pressure, either the front or the rear brakes will not be operating fully, which means it will take you longer to stop. Bring the vehicle to a safe stop and have the air brake system fixed before continuing.
How this test works
Start a quick test, drill one topic, or run the whole bank. After each answer you see why it is right, why the choice you picked is wrong, and the handbook page to reread. Questions you miss come back in the retry round until you get them right. Back to the Texas DMV guide.
