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CDL - COMBINATION VEHICLE PRACTICE TEST QUESTIONS WITH CORRECT ANSWERS 2025 A tractor with a(n) trailer requires the shortest amount of stopping distance . 1. empty 2. fully loaded 3. lightly loaded - CORRECT ANSWER-fully loaded The air leakage rate for a combination vehicle ( engine off, brakes on) should not be more t han psi per minute . 1.4 2.6 3, 2 - CORRECT ANSWER-4 If you do not do the final air brake check for air leaks and fix them before driving, 1. you could lose your brakes while driving 2. your fuel usage will increase 3. tire pressure will drop - CORRECT ANSWER-you could lose your brakes while driving Which part of the kingpin should the locking jaws close around? - CORRECT ANSWER- The shank Glad hands are used to connect the .... 1. kingpin from the trailer to the locking jaws of the fifth wheel 2. electrical lines from the tractor to the trailer 3. service and emergency air lines from the truck or tractor to the trailer - CORRECT ANSWER-service and emergency air lines from the truck or tractor to the trailer Trucks roll over more easily when fully loaded and are 1. ten times more likely to roll over in a crash than empty rigs 2. five times more likely to roll over in a crash than empty rigs 3. two times more likely to roll over in a crash than empty rigs - CORRECT ANSWER- ten times more likely to roll over in a crash than empty rigs In general, the higher your trucks center of gravity, the ... 1. easier it is to turn over 2. more stable it is when turning 3. easier it is to turn around corners - CORRECT ANSWER-easier it is to turn over You are driving a combination vehicle when the trailer breaks away, pulling apart both air li nes. You would expect the trailer brakes to come on and ... 1. the tractor to lose all air pressure 2. the tractor protection valve to close 3. the trailer supply valve to stay open - CORRECT ANSWER- the tractor protection valve to close When you drive a set of doubles, which shut-off valve must be closed in the last trailer? 1. Middle section 2. front section 3. back section - CORRECT ANSWER-back section 1. trailer tank pressure to be lost 2. trailer emergency brakes to come on 3. tractor spring brakes to lock on - CORRECT ANSWER-trailer emergency brakes to come on You are uncoupling a trailer. After you shut off the trailer air supply and lock the trailer bra kes, you should 1. immediately apply your tractor parking brakes 2. begin to lower the trailer landing gear 3. back up gently and ease pressure on the fifth wheel locking jaws - CORRECT ANSWER- back up gently to ease pressure on the fifth wheel locking jaws When should you use the hand valve to park a combination vehicle? 1. To park at loading docks 2. To park on a grade 3. never - CORRECT ANSWER-Never The front trailer supports are up, and the trailer is resting on the tractor. Make sure that 1. there is enough clearance between the upper and lower fifth wheel 2. there is enough clearance between the tractor frame and the landing gear 3. the safety latch is in the unlocked position - CORRECT ANSWER- there is enough clearance between the tractor frame and the landing gear The trailer hand valve works the trailer brakes. Which of these statements is true? 1. the foot brake sends air to all the brakes on the vehicle ( including the trailer(s)) 2. The trailer hand valve should be used only to test the trailer brakes 3. all the above - CORRECT ANSWER-all the above Where should the tractor be when you inspect the landing gear after uncoupling the trailer ? 1. With the fifth wheel directly beneath the kingpin 2. completely cleared from the trailer 3. with the tractor frame under the trailer - CORRECT ANSWER- with the tractor frame under the trailer After you lock the kingpin into the fifth wheel, you should check the connection by pulling 1. the tractor ahead gently with the trailer brakes locked 2. forward 50 feet, then turning right, and then left 3. the tractor ahead sharply to release the trailer brakes - CORRECT ANSWER- the tractor ahead gently with the trailer brakes locked At night, when a vehicle is carrying a load that extends four feet or more beyond the rear of the body, there must be at the extreme end of the load. 1. red lights 2. red flags 3. a red flag - CORRECT ANSWER-red lights Which type of truck-trailer combination has the greatest chance of a "crack-the- whip" rollover? 1. A tractor pulling three trailers 2. A single tractor trailer 3. A tractor pulling two trailers - CORRECT ANSWER-A tractor pulling 3 trailers Air and electrical lines from the tractor to the trailer should be... 1. pulled tight with very little slack When you are uncoupling a loaded trailer, lower the landing gear until it ... 1. reaches the ground 2. makes firm contact with the ground 3. makes contact with the ground, and leave the trailer off the fifth wheel - CORRECT ANSWER-makes firm contact with the ground How much space should there be between the upper and lower fifth wheel after coupling? 1. Just enough to see light through it 2. About 1/4 inch 3. None - CORRECT ANSWER-none After you have coupled the trailer, you should start to raise the landing gear by using 1. low gear 2. high gear 3. intermediate gear - CORRECT ANSWER-low gear The fifth wheel locking lever is not locked after the jaws close around the kingpin. This mea ns that 1. the parking lock is off and you may drive away 2. the coupling is not right and should be fixed before you drive the coupled unit 3. the trailer will not swivel on the fifth wheel - CORRECT ANSWER- the coupling is not right and should be fixed before you drive the coupled unit When checking the trailer emergency brakes, make sure that the tractor protection control valve is placed in the position. 1. normal 2. emergency 3. neutral - CORRECT ANSWER-emergency You should use chocks when parking a trailer without spring brakes because 1. if the air supply leaks away, there will be no brakes 2. some states require chocking of trailer wheels 3. you dont want the trailer rolling down a hill - CORRECT ANSWER- if the air supply leaks away, there will be no brakes You are uncoupling a trailer. After you shut off the trailer air supply and lock the trailer bra kes, you should 1. begin to lower the trailer landing gear 2. immediately apply your tractor parking brakes 3. back up gently to ease pressure on the fifth wheel locking jaw - CORRECT ANSWER- back up gently to ease pressure on the fifth wheel locking jaw While you are driving, your emergency air line breaks or gets pulled apart. The loss of press ure will cause the 1. air compressor to unload instead of pumping air 2. trailer emergency brakes to come on 3. trailer supply valve to open - CORRECT ANSWER-trailer emergency brakes to come on You are coupling a tractor to a semi- trailer. You have backed up but are not yet under it. Before backing under the semi trailer, you should hook up 1. the electrical service cable 2. nothing. Back up and lock the fifth wheel 3. The emergency and service air lines - CORRECT ANSWER- the emergency and service air lines 
