Missouri DOR CDL General Knowledge Practice Test 2
Test 2 of 5. Pick an answer for each question to see if it is right and why; your score appears at the end. You need 40 correct answers to pass, the same ratio as the real Missouri test.
- Questions50
- Correct to pass40
- Passing score80%
- Minimum age18 years
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1. Under federal rules, which commercial vehicles must stop at every railroad crossing before proceeding?
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Answer D: Passenger buses and placarded hazardous materials vehicles
Buses carrying passengers and vehicles required to display hazardous materials placards must stop at crossings, while other commercial vehicles slow and check.
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2. Which set of maneuvers makes up the basic control skills part of the commercial driving test?
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Answer D: Straight line backing, offset backing, parallel parking and alley docking
The basic control skills test is carried out off the road and consists of low speed exercises such as straight line backing, offset backing, parallel parking and the alley dock.
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3. How does overloading affect the way a vehicle drives?
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Answer C: It slows the vehicle on upgrades, makes stopping take longer and can overheat the brakes on downgrades
Extra weight demands more from the engine and the brakes, so the vehicle climbs slowly and needs much more distance to stop.
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4. You are about to back across a quiet street into a driveway. Which of these is good practice before you start to move?
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Answer B: Turn on the four-way flashers and sound the horn to alert anyone nearby
Warning other road users and pedestrians before a reverse maneuver gives them the chance to stop or move clear before the vehicle starts back.
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5. When should mirror adjustment be checked, and what should each mirror show?
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Answer B: Before every trip, with each mirror adjusted to show some part of the vehicle
Checking the mirrors before each trip and keeping a small part of the vehicle in view gives a reference point for judging distance behind and beside you.
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6. When is a road surface usually most slippery during a rain shower?
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Answer A: Just after the rain starts, when water mixes with oil and dirt on the surface
The first rain lifts oil and dust into a slick film that has not yet been washed away, so the road is more slippery than it will be later.
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7. How do you test for leaks in a hydraulic brake system during the pre-trip inspection?
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Answer A: Pump the pedal three times, then hold firm pressure for five seconds and make sure the pedal does not move
If the pedal sinks while you hold pressure, fluid is escaping or air is in the lines, and the vehicle must not be driven until the problem is repaired.
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8. Why is a leak in the exhaust system especially dangerous in cold weather?
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Answer A: Carbon monoxide can build up inside a closed cab
In winter the windows are shut and the heater is running, so exhaust gas that escapes early can reach the driver and cause drowsiness or worse.
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9. Your brakes have failed and you decide to use the parking brake to slow down. Why should you hold the release button or lever while doing so?
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Answer D: So you can release the brake at once if the wheels lock and the vehicle starts to skid
The parking brake can lock the wheels; keeping your hand on the release lets you let go the moment a skid starts and regain control.
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10. What happens to braking distance when speed is doubled?
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Answer C: It becomes about four times longer
Braking distance grows with the square of speed, so doubling the speed multiplies both the braking distance and the force of an impact by about four.
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11. What should be checked about the power steering system in the engine compartment?
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Answer D: That the fluid level is correct and the hoses and pump are not leaking
Losing power steering fluid means losing steering assistance, which can happen suddenly and makes a heavy vehicle very hard to turn.
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12. A doctor prescribes you a medicine that can cause drowsiness. What should you do?
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Answer A: Tell the doctor what you drive and not drive while affected
Both prescription and over the counter medicines can make a driver unsafe, so the medical professional must know the job and the driver must stay out of the seat while affected.
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13. On a multilane highway, which lane should a heavy vehicle normally use?
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Answer A: The right lane, except to pass or where signs direct otherwise
Keeping right leaves the faster lanes free and reduces the number of vehicles that have to move around a slower, heavier vehicle.
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14. Why is cargo often covered with a tarp?
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Answer C: To protect people from spilled cargo and to protect the cargo from weather
A cover keeps material from blowing or spilling onto the road and shields the load from rain and sun; it does not replace securement.
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15. What is checked about the engine cooling system during the engine compartment inspection?
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Answer C: That the coolant level is adequate and the radiator and hoses are not leaking
A low coolant level or a leaking hose leads to overheating, which can stop the vehicle in a place where stopping is dangerous.
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16. What must a written driver vehicle inspection report cover at the end of the day?
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Answer C: Any defect or deficiency that would affect safety or could cause a mechanical breakdown
The report identifies the vehicle and lists defects that affect safe operation or could lead to a breakdown, so they are repaired before the next trip.
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17. What is the danger of letting engine speed climb past the top of the rated rpm range before you shift?
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Answer B: You can damage the engine, so the shift should be made before that point
Every engine has a rated operating range; running above it can cause serious engine damage, so the upshift belongs at the top of that range, not beyond it.
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18. When should a driver add space beyond the basic following distance rule?
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Answer D: On slippery roads and whenever visibility is poor
The seconds rule is a minimum for good conditions, so rain, snow, darkness and heavy traffic all call for more space than that.
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19. A dispatcher tells you to take a trailer you believe is loaded badly enough to be unsafe. What should you do?
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Answer C: Refuse to move it until the load has been made safe
The driver may not operate a vehicle whose cargo is not properly distributed and secured, and an instruction from an employer does not change that.
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20. The brake pedal goes to the floor in a vehicle with hydraulic brakes. What can you do to build some braking pressure?
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Answer B: Pump the brake pedal rapidly, which may bring back enough pressure to slow the vehicle
Pumping can restore some hydraulic pressure; along with downshifting and the parking brake it is one of the ways to stop when the pedal fails.
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21. How does bracing differ from blocking when securing cargo?
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Answer B: Bracing runs from the upper part of the cargo to the floor or walls to keep it from moving, while blocking fits snugly against the cargo
Blocking is shaped to fit against the front, back or sides of a piece of cargo; bracing supports it from above so it cannot tip or shift.
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22. Loading heavy freight on top of lighter freight has what effect on the vehicle?
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Answer B: It raises the center of gravity and makes a rollover more likely
A high center of gravity lets the vehicle tip more easily in curves or during a sudden swerve.
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23. You are asked to drive a truck loaded with enough hazardous materials to require placards. What must you have?
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Answer C: A hazardous materials endorsement on your commercial driver license
Driving a vehicle that must be placarded requires the H endorsement, which involves a separate knowledge test and a security background check.
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24. Which of these counts as a serious traffic violation for a commercial driver license holder?
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Answer C: Speeding 15 miles per hour or more above the limit
Excessive speeding, reckless driving, improper lane changes, following too closely and texting while driving are all serious traffic violations.
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25. What is the driver responsible for when a load is covered with a tarp?
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Answer C: Fastening it so it cannot flap free, block a mirror, or come off in the wind
A tarp that works loose can tear away, block the driver view or the view of others, and become a hazard for the traffic behind.
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26. You have just passed another vehicle on a two lane road. What tells you it is safe to return to your lane?
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Answer B: You can see the whole front of that vehicle in your right mirror
Seeing the entire front of the vehicle you passed in your mirror proves you are far enough ahead to move back over without cutting the driver off.
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27. How long is a Missouri commercial learner's permit valid, and can it be renewed?
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Answer B: One year at most, and it cannot be renewed
A Missouri commercial learner's permit is issued for up to one year (360 days) and cannot be renewed; a driver who runs out of time must retake the knowledge tests.
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28. Under federal safety rules, what must the driver of a commercial vehicle do before starting a trip?
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Answer A: Be satisfied that the vehicle is in safe operating condition
The driver is responsible for inspecting the vehicle and must be satisfied it is in safe operating condition before the trip begins.
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29. At 55 mph on dry pavement with good brakes, total stopping distance for a loaded heavy vehicle is roughly what?
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Answer B: About 400 feet or more
Perception, reaction, and braking together add up to roughly 400 feet or more, farther than the length of a football field.
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30. Part of looking well ahead is planning an out. What does that mean?
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Answer B: Keeping an escape path in mind in case traffic stops suddenly
Because a heavy vehicle often cannot stop in time, good drivers continuously note where they could steer if the space ahead closes.
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31. During a trip you stop for a break. Which items should you check before driving on?
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Answer B: Tires, wheels and rims, brakes, lights, reflectors, electrical connections and cargo securement
Critical items can change during a trip, so each stop is used to recheck the tires, wheels, brakes, lights, connections and cargo.
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32. In very hot weather, how often should you check the tires during a trip?
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Answer D: About every two hours or every 100 miles
Heat raises tire pressure and can lead to blowouts, so tires are checked about every two hours or 100 miles when it is very hot.
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33. You need to check your route on a navigation device. What is the correct approach?
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Answer D: Set it before the trip or after you have parked
Route programming is planning work, and it belongs to the time before the wheels turn or after the vehicle is safely parked off the roadway.
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34. Which commercial vehicles must stop at every official Missouri weigh station?
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Answer C: Every one except those licensed for 18,000 pounds or less
Missouri requires every commercial motor vehicle to stop at each official weigh station except those licensed for 18,000 pounds or less, which may still be directed to stop.
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35. What is the minimum tread depth for tires in positions other than the steering axle?
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Answer A: 2/32 inch
Drive and trailer tires must keep at least 2/32 inch of tread in a major groove, measured away from tie bars and fillets.
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36. Why should you avoid using your lights to tell a following driver that it is safe to pass you?
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Answer B: You may misjudge the gap and the driver will act on your signal
The manual warns against signaling others to pass, because the responsibility for a head-on crash then rests on a judgment you could easily get wrong.
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37. Which situations call for a mirror check in a commercial vehicle?
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Answer A: Every lane change, turn, merge and tight maneuver
Mirrors must be checked regularly and always before, during and after any movement that changes the path of the vehicle.
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38. When should the horn of a commercial vehicle be used?
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Answer C: Only when it is needed to avoid a crash
An air horn is loud enough to startle other road users, so it is a warning device rather than a way to comment on other drivers.
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39. What is the coupling device weight rating on a vehicle?
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Answer A: The most weight that the coupling on the vehicle is rated to pull
The coupling device rating is a limit on how much weight the coupling may tow, and it is one of the ratings that has to be respected when a combination is loaded.
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40. What tells you that an air suspension bag has a problem?
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Answer B: The bag is leaking or damaged, or the vehicle sits unevenly on that side
An air bag that leaks or is cut lets that corner of the vehicle settle, which throws the load onto the other suspension parts and changes the ride height.
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41. Before starting a trip, what must the driver confirm about the weight of the loaded vehicle?
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Answer A: That it is within the legal gross and axle limits for the route being driven
Overweight vehicles brake poorly, damage tires and suspension components, and can be put out of service at a scale, so weight is checked before the wheels turn.
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42. What extra consequence can a commercial driver face for violating Missouri's electronic communication device law?
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Answer D: Disqualification of the commercial driving privilege
Missouri commercial drivers who violate the electronic communication device law may be disqualified, on top of the fines that apply to every driver.
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43. What should the ammeter or voltmeter show once the engine is running?
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Answer D: A reading in the normal charging range
With the engine running, the alternator should be charging; a discharge reading or an abnormal charge level means an electrical fault.
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44. For a modern truck with low-friction parts and a streamlined shape, which gear should be used going down a grade?
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Answer D: A gear lower than the one needed to climb the same grade
Newer trucks roll more freely than older ones, so the old rule of using the climbing gear no longer holds; a lower gear is needed for enough engine braking.
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45. You are stopped in a line of traffic behind a car. How much space should you leave in front of you?
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Answer C: Enough to see where the rear tires of that car meet the road
That amount of space lets you pull around the vehicle ahead if it stalls and absorbs some of the shock if you are struck from behind.
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46. An article of cargo has been blocked so that it cannot move forward. How many tiedowns does the federal rule call for?
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Answer A: One tiedown for every 10 feet of article length, or any part of that
Blocking against forward movement lowers the requirement to one tiedown per 10 feet of length or fraction of 10 feet.
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47. You are strapping down a load with sharp metal edges on a flatbed. What should you use?
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Answer D: Edge protection between the strap and the sharp edges so the tiedown is not cut
Sharp edges cut or wear through a strap under tension, so edge protectors are required wherever a tiedown could be damaged.
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48. Where is the yellow antilock brake malfunction lamp on a trailer, and what does it mean if it stays lit?
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Answer D: On the left side, at the front or rear corner, and it means the antilock function may not be working
Trailers carry the yellow lamp on the left side, and a lamp that stays on after the bulb check means the antilock function may be lost even though the normal brakes still work.
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49. What is checked in step six of the seven-step method?
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Answer D: The turn signals and the stop lights, checked from outside the vehicle
Step six returns to the cab to switch on the signal and stop lamps, then checks each one from outside, because those lamps are not lit during the earlier light check.
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50. Which windshield condition should be reported during the inspection?
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Answer B: Cracks or dirt that get in the way of your view of the road
The windshield must give a clear view; damage or grime in the driver line of sight is a safety defect.