Missouri DOR CDL General Knowledge Practice Test 10
- Questions50
- Correct to pass40
- Passing score80%
- Minimum age18 years
-
1. You have finished a lane change in a vehicle whose turn signal does not cancel by itself. What must you do?
Show answer
Answer D: Turn the signal off yourself
A signal left running tells other drivers you are about to move again, and they may act on that false information.
-
2. Why does extra weight make a long downgrade more dangerous even when the brakes are in good order?
Show answer
Answer B: Gravity adds to the momentum and the brakes heat up faster
The heavier the vehicle, the more energy the brakes must turn into heat, and heat is exactly what makes brakes fade on a long descent.
-
3. What is the purpose of blocking placed against cargo on a trailer deck?
Show answer
Answer B: To fill the space around the cargo so it cannot slide
Blocking is shaped to fit snugly against the cargo and fastened to the deck, removing the room the load would need in order to move.
-
4. Dry bulk tanks call for extra caution mainly because of what?
Show answer
Answer C: A high center of gravity combined with a load that can shift
Dry bulk loads ride high and can move inside the tank, which makes the vehicle easier to tip in a curve.
-
5. How does a typical escape ramp stop a runaway vehicle?
Show answer
Answer B: With a bed of loose gravel or sand, often on an upgrade
Escape ramps use deep loose material, usually combined with a rising grade, so the vehicle is slowed gradually instead of being stopped by impact.
-
6. You drive a 40 foot straight truck at 50 miles per hour in good conditions. What following distance does the rule of thumb call for?
Show answer
Answer A: 5 seconds
One second for every 10 feet of vehicle length gives 4 seconds, and one extra second is added for speeds above 40 miles per hour.
-
7. What speed and gear should be used when backing a large vehicle?
Show answer
Answer B: As slowly as possible, in the lowest reverse gear
Backing slowly in the lowest reverse gear keeps the vehicle under precise control and leaves time to correct the path.
-
8. Your vehicle begins to hydroplane on a wet road. What should you do?
Show answer
Answer B: Release the accelerator and push in the clutch so the wheels can turn freely and regain grip
Hydroplaning tires are riding on water; slowing without braking lets them settle back onto the road and grip again.
-
9. What information does an inspection decal on a commercial vehicle carry?
Show answer
Answer B: The date of the inspection, where the inspection report is kept, and information identifying the vehicle
The decal shows when the inspection was done, the name and address of the entity that holds the inspection report, and which vehicle it belongs to, so an officer can confirm the inspection at a glance.
-
10. The shipper hands you the placards for a load that needs them. Who puts them on the vehicle?
Show answer
Answer C: The driver, who must also make sure they are the correct ones and are readable
The shipper supplies the placards, but it is the driver who must place them on the vehicle and confirm that they match the load and can be read.
-
11. On a one way street or a divided highway, where are the warning devices placed?
Show answer
Answer B: About 10 feet, 100 feet and 200 feet back toward the approaching traffic
When traffic can only come from one side, all three devices are spread out behind the vehicle to give approaching drivers a longer warning.
-
12. You find a defect during the pre-trip inspection. What must happen before the vehicle is driven?
Show answer
Answer C: It must be repaired, or the vehicle must not be driven
Writing a defect down does not make the vehicle safe; a defect that affects safe operation has to be corrected before the trip starts.
-
13. During the walkaround you find the reflective conspicuity tape along the trailer caked with road grime. What should you do?
Show answer
Answer B: Clean it, because dirty reflective material cannot make the trailer visible at night
Reflective sheeting only works if light can reach it and bounce back, so a dirty strip leaves the trailer effectively unmarked to approaching traffic.
-
14. Where should a driver expect fog to form first?
Show answer
Answer D: In low ground, near water and in valleys
Cool moist air settles in low places, so fog patches appear in hollows, river valleys and near lakes before they appear anywhere else.
-
15. What must the motor carrier do about a defect listed on a driver vehicle inspection report?
Show answer
Answer D: Repair it, or certify that repair is not needed, before the vehicle is dispatched again
A reported defect must be corrected, or certified as not needing correction, and that certification is what the next driver reads before taking the vehicle.
-
16. How long is a Missouri commercial learner's permit valid, and can it be renewed?
Show answer
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.
-
17. What is the purpose of the torque rods or radius rods you check on the suspension?
Show answer
Answer A: They hold the axle in alignment with the frame under braking and acceleration
Torque rods resist the twisting and fore and aft forces on the axle, so a cracked or missing rod lets the axle move out of alignment.
-
18. A driver behind you wants to pass and you can see that the road ahead is clear. What should you do?
Show answer
Answer B: Do not signal the other driver to pass; let that driver decide when it is safe
Directing other drivers can cause a crash if you misjudge the gap, so leave the decision to the driver who is passing.
-
19. Your speedometer stops working during the pre-trip check. How should it be treated?
Show answer
Answer D: As a defect, because the driver cannot judge and control speed without it
A working speedometer is required equipment, because judging speed by feel in a heavy vehicle is unreliable and speed governs stopping distance.
-
20. At what time of day do drowsy driving crashes occur most often?
Show answer
Answer A: Between midnight and 6 a.m.
The body clock makes people sleepiest in the early morning hours, which is when most fatigue-related crashes happen.
-
21. Why must tiedowns be rechecked during a trip even when they were tight at the start?
Show answer
Answer C: Road vibration and cargo movement can loosen them as the miles go by
Straps and chains settle and loosen as the vehicle bounces and the cargo shifts slightly, so the load must be rechecked at the required intervals.
-
22. Which document must be available to show that the annual inspection was carried out?
Show answer
Answer C: The inspection report or a copy of it, or a decal displayed on the vehicle
Proof of the periodic inspection travels with the vehicle, either as the report itself or as the decal fixed where an inspector can see it.
-
23. Why does a load of hanging meat in a refrigerated trailer require special care in curves?
Show answer
Answer D: The meat swings and has a high center of gravity, which makes the trailer unstable
Hanging meat is heavy, sits high and swings, so the trailer can tip in a curve or on a ramp taken at normal speed.
-
24. What is the correct way to make a right turn in a long vehicle?
Show answer
Answer D: Keep the rear of the vehicle close to the curb and swing wide only as you complete the turn
Swinging left before a right turn invites another driver to move into the gap on your right, so any extra width is taken as the turn is finished.
-
25. A tire has a cut deep enough to expose the body ply or the belt material. What does that mean?
Show answer
Answer D: The vehicle must not be driven on that tire
Once the structural plies are exposed the casing has lost its strength, and federal rules treat that tire as unfit for the road.
-
26. In a vehicle with a manual transmission, when should the clutch be pushed in during a normal stop?
Show answer
Answer A: Just before the engine would stall, when the vehicle is nearly stopped
Staying in gear until the last moment keeps engine braking and steady control, so the clutch goes down only when the engine is about to drop below idle.
-
27. What is the payload of a truck?
Show answer
Answer C: The weight of the cargo the vehicle is carrying, that is the loaded weight less the empty weight
Payload is what is left of the legal or rated weight once the weight of the empty vehicle is taken off, and it is the weight of cargo that can be carried.
-
28. Which factors determine a safe speed for a long, steep downgrade?
Show answer
Answer C: The steepness and length of the grade, the weight of the vehicle and cargo, and the road and weather conditions
Gravity, weight and traction all decide how fast a heavy vehicle can safely descend, which is why signs often post lower speeds for trucks on grades.
-
29. You pick up a sealed trailer at a shipper. What should you check before leaving the dock?
Show answer
Answer B: That the seal number matches the paperwork and that the doors are properly closed
You cannot look at a sealed load, but you can confirm that the seal is intact, that its number matches the documents and that the doors are secure.
-
30. How should a commercial driver treat the speed posted for a curve?
Show answer
Answer B: As a limit set for cars in good conditions, so a heavy or tall load calls for a lower speed
Posted curve speeds are based on passenger vehicles in good conditions, and a tall or heavy load can roll over well below that speed.
-
31. Besides being uncomfortable, what can a series of hard, jerky brake applications do to a loaded combination?
Show answer
Answer A: Shift the load and push the trailer out of line behind the tractor
Sudden, uneven braking can move cargo forward and upset the alignment of a trailer, which is why stops should be made smoothly.
-
32. On a set of dual tires, which condition must be reported as a defect?
Show answer
Answer D: The two tires are touching each other or rubbing on part of the vehicle
Duals that touch each other or the vehicle overheat and wear quickly, so they must be separated by proper spacing and inflation before driving.
-
33. Besides the hours when the law requires them, when should headlights be switched on?
Show answer
Answer A: Any time visibility is poor, such as in rain, fog or at dusk
Headlights are used to be seen as much as to see, so they belong on whenever light or weather makes the vehicle harder to spot.
-
34. Why should you avoid using your lights to tell a following driver that it is safe to pass you?
Show answer
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.
-
35. Using the snub braking method on a downgrade, when does the driver release the brakes?
Show answer
Answer A: After speed has dropped about 5 mph below the safe speed
The driver brakes firmly to about 5 mph under the chosen safe speed, releases to let the brakes cool, then repeats when the safe speed returns.
-
36. A hazard suddenly appears ahead and you must act. Which is usually the faster way to avoid it in a heavy vehicle?
Show answer
Answer B: Steering around it, because you can usually turn faster than you can stop
Stopping distance at speed is very long, so a quick turn out of the way, when there is room, avoids the crash sooner than braking.
-
37. During a right turn in a tractor-trailer, what are you looking for in the right hand mirror?
Show answer
Answer B: Whether the trailer will clear the curb and whether anything has moved alongside you
The right mirror is what tells you how close the trailer wheels are running to the curb and whether a vehicle or a cyclist has slipped into the space on your right.
-
38. You miss a gear while double clutching and the transmission is stuck in neutral. What should you do?
Show answer
Answer B: Return to neutral, release the clutch, bring engine speed to match road speed and try again
Forcing the lever damages the gears; matching the engine speed to the road speed lets the gear engage cleanly on the next try.
-
39. What does the tachometer on the dashboard of a heavy truck show?
Show answer
Answer D: How fast the engine is turning, in revolutions per minute
The tachometer reads engine speed in rpm, which is what a driver uses to judge shift points in a vehicle with a manual transmission.
-
40. Two vehicles of exactly the same length make a right turn, one gently and one very tightly. What is the effect on off-tracking?
Show answer
Answer A: Turning more sharply increases off-tracking, so the tight turn needs more room
Off-tracking depends on both the length of the vehicle and the sharpness of the turn; a tighter corner brings the rear wheels further inside the path of the front wheels.
-
41. What are you checking when you look at the batteries during the engine compartment inspection?
Show answer
Answer D: That they are securely mounted, the connections are tight and free of corrosion, and the caps are in place
Loose or corroded batteries can fail or short out, so the mount, cables, terminals and vent caps are all part of the check.
-
42. You want to check whether a tire on your truck is properly inflated. What is the correct method?
Show answer
Answer A: Measure the pressure with a tire gauge
Only a tire gauge tells you the actual pressure; a tire can look and sound normal while being badly underinflated.
-
43. What is the purpose of the header board, or headache rack, that you inspect behind the cab?
Show answer
Answer A: It protects the driver from cargo that shifts forward during a hard stop
In a hard stop the load keeps moving forward, and the header board is the barrier between that load and the back of the cab.
-
44. How much free play in the steering wheel is enough to make a vehicle hard to steer and should be reported?
Show answer
Answer B: More than 10 degrees, roughly 2 inches of movement at the rim of a 20 inch wheel
Excess play means steering input is lost before the wheels respond, and more than about 10 degrees is treated as a defect.
-
45. Most rollovers of loaded trucks on exit and entrance ramps happen for which reason?
Show answer
Answer B: The ramp was taken faster than the load could tolerate
A posted ramp speed is set for cars, and a loaded trailer with a high center of gravity can roll at a speed a car would take easily.
-
46. Which vehicles are most likely to get hung up on a raised railroad crossing?
Show answer
Answer A: Low-slung units such as car carriers and lowboys
Vehicles with low ground clearance or a long wheelbase can bottom out on a humped crossing and become stuck on the tracks.
-
47. What frame defects are you looking for during the walkaround?
Show answer
Answer A: Cracks, bends or broken cross members
The frame carries the whole load, so cracked or bent rails and broken cross members are serious structural defects.
-
48. Who must sign a driver vehicle inspection report?
Show answer
Answer D: The driver who prepared it
The report is the driver statement about the condition of the vehicle at the end of the day, so the driver signs it.
-
49. Why must the downshift be finished before you reach a steep downgrade or a sharp curve rather than during it?
Show answer
Answer D: Because once your speed is too high you may not get into any gear at all
If you wait until speed has built up, the lower gear may refuse to engage and you can be left in neutral with no engine braking at all.
-
50. What does the suspension system weight rating tell the driver?
Show answer
Answer A: The maximum weight that the manufacturer says the suspension can carry
Like tires and axles, suspensions have a manufacturer capacity, and loading beyond it can damage springs and air bags.