CDL Combination Vehicle Practice Test Questions & Answers Latest Updated 2024/2025 (GRADED)

You supply air to the trailer tanks by: A. pushing in the trailer air supply valve B. pulling out the trailer air supply valve C. connecting the service air line 2. Loss of air pressure in the emergency line causes: A. the relay valves to close B. an increase in air pressure to the service line C. the trailer's emergency brakes to come on 3. A tractor with a __ trailer requires the shortest amount of stopping distance. A. empty B. lightly loaded C. fully loaded 4. Which of these statements is true? A. the brake and suspension of combination vehicles work best with a light load CDL Combination Vehicle Practice Test Questions & Answers Latest Updated 2024/2025 B. light vehicles need more braking power to stop than heavy ones C. bobtails tractors can take longer to stop than fully loaded combination vehicles 5. If you cannot make a right turn without swinging into another lane, you should: A. swing wide before you make the turn B. turn wide as you complete the turn C. not make that turn. Go to another place to turn. 6. The tractor protection valve will close and the trailer emergency brakes will come on when there is a major leak in what air line? A. service B. emergency C. parking 7. Off tracking or "cheating" causes which of these to follow the widest path while making a turn? A. 3 axle tractor towing a 45 foot trailer B. 3 axle tractor towing two 27 foot trailers C. A bobtail tractor 8. If your vehicle gets stuck on a railroad crossing, you should: A. use reverse to back of the tracks B. get out of the vehicle and away from the tracks C. turn on your 4-way flashers 9. When driving a set of double trailers, it is necessary to close shut-off valves on some trailers. Where are these valves located? A. in the front of trailers B. in the middle C. at the back of trailers used to tow other trailers 10. Before you back under a trailer, make sure of what? A. the trailer brakes are locked B. the air supply knob is in C. the air brakes are of 11. To unlock the fifth wheel, you pull the handle to what position? A. open B. neutral C. closed 12. After connecting the air lines but before backing under the trailer, you should: A. supply air to the trailer, then pull out the trailer air supply valve B. make sure that the trailer brakes are off C. walk around the rig to be sure it is clear 13. You are coupling a tractor to a semi-trailer and you have backed up but are not yet under it. What should you hook up before backing under it? A. the emergency and service air lines B. the electric line C. nothing, back up and lock the fifth wheel 14. You are coupling a tractor to a trailer. The trailer is at the right height when: A. the kingpin is about 1 inch above the fifth wheel B. the end of the kingpin is even with the top of the fifth wheel C. the trailer is raised slightly when the tractor is backed under it 15. Why should you connect the air lines to a dummy coupler when they are not in use? A. the connected circuit becomes a back up air tank B. it will keep dirt and water out of the lines C. if you don't you will never build pressure in the system 16. The air leakage rate for a combination vehicle with the engine off and the brakes off should be less than___ per minute. A. 1 PSI B. 2 PSI C. 3 PSI 17. Air and electric lines from the tractor to the trailer should be: A. pulled tight with very little slack B. secured properly with enough slack for turns C. resting on the frame of the tractor 18. Air brake equipped trailers made before 1975: A. often do not have spring brakes B. usually need a glad hand converter C. cannot be legally operated on interstate highways 19. The hand valve should be used: A. only with the foot pedal B. to test the trailer brakes C. as a parking brake 20. The air leakage rate for a combination vehicle with the engine off and the brakes on should be less than_ per minute. A. 2 PSI B. 3 PSI C. 4 PSI 21. Your emergency line breaks or gets pulled apart while driving. The loss of pressure will cause the: A. emergency trailer brakes to come on B. air compressor to unload instead of pumping C. trailer supply valve to open 22. You have pushed in the trailer air supply valve. You should not move the vehicle until the whole system is: A. empty B. at normal pressure C. between 60 and 80 PSI 23. When should you use the hand valve to park a combination vehicle? A. to park at loading docks B. to park on a grade C. never 24. The best way to tell that your trailer has started to skid is to: A. hear the wheels skidding B. see it in your mirrors C. feel the cab pulling 25. A trailer is most likely to jackknife when it is: A. loaded to full capacity B. over loaded