{"@context":"http://schema.org","@type":"Quiz","Name":"Combination Vehicle CDL Practice Test Version 2","Description":"This CDL Practice test features combination vehicles questions to get you ready for your commercial learners permit exam. Roehl offers multiple free practice CDL tests to help you get cdl training.","HasPart":[{"@type":"Question","Text":"What consideration should be made when you park a trailer that doesn't have spring brakes?","AcceptedAnswer":{"@type":"Answer","Text":" Use wheel chocks","AnswerExplanation":{"@type":"Comment","Text":"When you want to park your trailers and don't have spring brakes you must use wheel chocks."}}},{"@type":"Question","Text":"You should not back a tractor under a trailer until the whole air system is:","AcceptedAnswer":{"@type":"Answer","Text":" At normal pressure","AnswerExplanation":{"@type":"Comment","Text":"Do not back a tractor under a trailer until the whole air system is at normal pressure."}}},{"@type":"Question","Text":"Which type of truck-trailer combination has the greatest chance of a 'crack-the-whip' rollover?","AcceptedAnswer":{"@type":"Answer","Text":" A tractor pulling three trailers","AnswerExplanation":{"@type":"Comment","Text":"A tractor pulling three trailers has the greatest chance of a crack-the-whip rollover"}}},{"@type":"Question","Text":"A trailer jackknife is likely to happen when:","AcceptedAnswer":{"@type":"Answer","Text":" The wheels of the trailer lock up","AnswerExplanation":{"@type":"Comment","Text":"The wheels of the trailer will lock up. When the wheels of the trailer lock up the trailer may swing around resulting in a trailer jackknife. Trailer jackknifes are more likely to happen when the trailer is empty or lightly loaded."}}},{"@type":"Question","Text":"When doing an inspection, which of the following would best describe a working landing gear?","AcceptedAnswer":{"@type":"Answer","Text":" Fully raised and not bent","AnswerExplanation":{"@type":"Comment","Text":"When doing an inspection, the landing gear needs to be fully raised and not bent."}}},{"@type":"Question","Text":"What are trailer air tanks used for?","AcceptedAnswer":{"@type":"Answer","Text":" To supply air pressure to the trailer brakes","AnswerExplanation":{"@type":"Comment","Text":"Trailer air tanks are used to supply air pressure to trailer brakes through relay valves"}}},{"@type":"Question","Text":"How many times should you drain the air tanks?","AcceptedAnswer":{"@type":"Answer","Text":"Everyday","AnswerExplanation":{"@type":"Comment","Text":"You should drain the air tanks every day. Air tanks must be drained every day to prevent all the water from building up."}}},{"@type":"Question","Text":"What does the trailer hand valve do?","AcceptedAnswer":{"@type":"Answer","Text":" It tests the trailer brakes","AnswerExplanation":{"@type":"Comment","Text":"The trailer hand valve is used to work the brakes on a trailer. It should not be used while driving as it can cause the trailer to skid."}}},{"@type":"Question","Text":"If the tractor protection valve malfunctions, which of the following may occur?","AcceptedAnswer":{"@type":"Answer","Text":" A leak or trailer break away could drain all the air from the brake system","AnswerExplanation":{"@type":"Comment","Text":"The tractor protection valve's purpose is to keep air in the brake system in case the trailer breaks away or develops a bad leak. If the tractor protection valve malfunctions, then air could be drained away from the brake system."}}},{"@type":"Question","Text":"What is the other name for the shut-off valves?","AcceptedAnswer":{"@type":"Answer","Text":" Cut-out cocks","AnswerExplanation":{"@type":"Comment","Text":"Shut-off valves are also known as cut-out cocks."}}},{"@type":"Question","Text":"Which shut-off valves should remain closed?","AcceptedAnswer":{"@type":"Answer","Text":" The valves at the back of the last trailer should remain closed","AnswerExplanation":{"@type":"Comment","Text":"All shut-off valves should be in the open position except the ones at the back of the last trailer."}}},{"@type":"Question","Text":"A fully loaded rig is _____ times more likely to roll over in a crash than an empty rig.","AcceptedAnswer":{"@type":"Answer","Text":"10","AnswerExplanation":{"@type":"Comment","Text":"When a truck has cargo, the center of gravity moves higher which increases the likelihood of rollover by 10 times."}}},{"@type":"Question","Text":"What should you do to prevent the crack-the-whip effect?","AcceptedAnswer":{"@type":"Answer","Text":" Steer gently and smoothly when pulling trailers","AnswerExplanation":{"@type":"Comment","Text":"As the crack-the-whip effect is unique to combination vehicles, you will have better control of the truck and any attached trailers when you steer gently and smoothly. Sudden turns, lane changes, etc. can cause the crack-the-whip effect and cause your trailers to turn over."}}},{"@type":"Question","Text":"What causes the crack-whip effect?","AcceptedAnswer":{"@type":"Answer","Text":" Rearward amplification","AnswerExplanation":{"@type":"Comment","Text":"When a truck has one or more trailers attached to it the crack-the-whip effect occurs due to rearward amplification. The more trailers there are the more likely than the rear trailer is to turn over."}}},{"@type":"Question","Text":"What happens if the trailer height is too high?","AcceptedAnswer":{"@type":"Answer","Text":" The trailer may not couple correctly","AnswerExplanation":{"@type":"Comment","Text":"If the trailer height for coupling tractor semi trailers is too high then the trailer may not couple correctly."}}},{"@type":"Question","Text":"Which type of vehicle is harder to control while stopping?","AcceptedAnswer":{"@type":"Answer","Text":" Larger combination vehicles that have no cargo in the trailers","AnswerExplanation":{"@type":"Comment","Text":"When a truck is empty, the stiff suspension and strong brakes, combined with limited traction can cause the rear wheels of a trailer to lock up. This can cause it to skid or swing out and hit other vehicles."}}},{"@type":"Question","Text":"What is the emergency air line?","AcceptedAnswer":{"@type":"Answer","Text":" It is an air line that supplies air to trailer air tanks and controls emergency brakes","AnswerExplanation":{"@type":"Comment","Text":"The emergency air line is used for two purposes. It supplies air to trailer air tanks and controls emergency brakes on combination vehicles."}}},{"@type":"Question","Text":"When should you use the hand valve to park a combination vehicle?","AcceptedAnswer":{"@type":"Answer","Text":"Never","AnswerExplanation":{"@type":"Comment","Text":"Never use the hand valve to park a combination vehicle because the air may leak out unlocking the brakes. Always use the parking brakes when parking."}}},{"@type":"Question","Text":"Which of the following is the best action you could take when the parking brakes don't release?","AcceptedAnswer":{"@type":"Answer","Text":" Check the air line connections","AnswerExplanation":{"@type":"Comment","Text":"Sometimes, the services and emergency air lines can be switched up, so you need to check the air line connections to ensure that the air lines are connected to the right places. If not, then the air used to release the parking brakes will not be available."}}},{"@type":"Question","Text":"What is the first thing you should do to prevent a trailer skid?","AcceptedAnswer":{"@type":"Answer","Text":" Maintain a constant speed to adjust the truck and trailer in a smooth fashion","AnswerExplanation":{"@type":"Comment","Text":"The best way to prevent a skid is to maintain a constant speed and make smooth adjustments. Slamming on the breaks or swerving may cause you to skid or jackknife."}}}]}