District of Columbia DC DMV CDL General Knowledge Practice Test 6
- Questions50
- Correct to pass40
- Passing score80%
- Minimum age18 years
-
1. 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.
-
2. You pick up a trailer that another driver dropped in the yard. What must you do before pulling it?
Show answer
Answer B: Inspect it yourself, because you are responsible for the whole vehicle you drive
Responsibility follows the driver who moves the vehicle, and a trailer that has stood in a yard may have lost air, developed a flat tire or been damaged.
-
3. How far ahead can a driver see with low beams and with high beams?
Show answer
Answer C: About 250 feet with low beams and about 350 to 500 feet with high beams
Low beams reach roughly 250 feet and high beams roughly 350 to 500 feet, and speed at night has to stay inside the distance the lights really show.
-
4. Taking your eyes off the road for about five seconds at highway speed means traveling roughly how far unseen?
Show answer
Answer A: About the length of a football field
At highway speed a five second glance away covers roughly 100 yards, which is far more road than any driver can afford to travel blind.
-
5. Under federal rules, what is required of a commercial driver who wants to use a mobile phone while driving?
Show answer
Answer B: The phone must be hands-free and started with no more than a single button press, and it must not be held
Federal rules ban texting and hand-held phone use while driving a commercial vehicle; reaching for, holding or dialing a phone is a violation.
-
6. A commercial vehicle stops on the shoulder of a one-way or divided highway. Where do the three warning devices go?
Show answer
Answer A: At 10 feet, 100 feet, and 200 feet back toward approaching traffic
Traffic arrives from one direction only, so all three devices are set back toward it at 10, 100, and 200 feet, and they must be out within ten minutes.
-
7. An unblocked article is 8 feet long and weighs 900 pounds. How many tiedowns does the federal rule require?
Show answer
Answer B: Two
Only an article that is 5 feet or shorter and 1,100 pounds or lighter can be held with a single tiedown; anything longer than 5 feet needs at least two whatever it weighs.
-
8. 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.
-
9. You are inspecting the vehicle alone and need to confirm that the stop lights work. Which method is correct?
Show answer
Answer A: Have a helper press the brake pedal, or apply the brake in a way that keeps it on while you check from outside
Stop lights are checked from outside the vehicle while the brakes are applied, so a helper or a brake held on is needed.
-
10. When traction is poor, such as on packed snow, how should you speed up?
Show answer
Answer C: Very gradually, so the drive wheels do not spin
Gentle throttle keeps the drive wheels from breaking traction, because spinning wheels give up both grip and directional control.
-
11. Why should a large vehicle be accelerated smoothly and gradually?
Show answer
Answer A: Rough acceleration can damage the drivetrain and, on a combination, the coupling
Jerky throttle inputs put shock loads through the driveline and the coupling, which causes mechanical damage over time.
-
12. 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.
-
13. What happens to braking performance if oil or grease reaches a brake lining?
Show answer
Answer B: That brake loses much of its effect and the vehicle can pull to one side
A contaminated lining cannot grip the drum, so that wheel contributes little braking and the vehicle pulls toward the side that is still working.
-
14. A driver snores heavily, stops breathing briefly during the night and is tired all day despite long hours in bed. What should be suspected?
Show answer
Answer B: Sleep apnea
Sleep apnea repeatedly interrupts breathing during sleep, so the driver never gets true rest and stays dangerously drowsy during the day.
-
15. Why should both outside mirrors be checked over and over while backing?
Show answer
Answer B: Each mirror covers only part of the path and neither covers the blind spots, so people and objects can appear without warning
Working both mirrors in turn is the only way to follow the whole path of a vehicle you cannot see behind.
-
16. 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.
-
17. 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.
-
18. Why does a heavy vehicle need a much larger gap than a car in order to cross or enter traffic?
Show answer
Answer C: Because it accelerates slowly and needs far more road and time to clear the intersection
Slow acceleration combined with the length of the vehicle means a gap that would feel comfortable in a car is nowhere near enough.
-
19. Does the federal texting ban apply to a company dispatching device mounted in the cab?
Show answer
Answer B: Yes, entering or reading text on it while driving is banned
The rule is written around the act of reading or entering text on any electronic device, not around who owns the device.
-
20. During the walkaround inspection, where does the driver normally start and how does the check proceed?
Show answer
Answer C: At the left front of the vehicle, working around it in a set order that returns to the cab
The walkaround follows the same route every time, starting at the left front and circling the vehicle, so that nothing is skipped when the driver is tired or rushed.
-
21. Which items belong to the trailer part of the walkaround inspection?
Show answer
Answer D: Landing gear, doors, tires, wheels, lights, reflectors, frame and cargo securement
The trailer has its own running gear, lighting, structure and load, and all of it is the responsibility of the driver pulling it.
-
22. What color must the clearance and side marker lamps and reflectors at the front of a trailer be?
Show answer
Answer A: Amber
Amber marks the front and the forward part of the sides of a vehicle, while red marks the rear, so another driver can tell which way the vehicle is facing.
-
23. In the seven-step method, what comes immediately after starting the engine and inspecting inside the cab?
Show answer
Answer D: Turn off the engine and check the lights
Step four shuts the engine down and switches on the lamps needed for driving so the driver can leave the cab and confirm they actually work.
-
24. Besides slowing down, which technique most reduces the risk of a skid on a snow covered road?
Show answer
Answer B: Make every steering, braking and speed change gradual
Traction is limited on snow, and sudden inputs demand more grip than the surface can supply, so smoothness is what keeps the tires attached to the road.
-
25. A 60 foot combination traveling above 40 mph should hold how many seconds of following distance?
Show answer
Answer D: Seven seconds
Six seconds cover the 60 feet of vehicle length, and one extra second is added because the speed is above 40 mph.
-
26. What condition should the fifth wheel be in before you back under a trailer?
Show answer
Answer C: Jaws open, plate greased, and the fifth wheel tilted down toward the rear
The jaws have to be open to take the kingpin, the plate must be lubricated to prevent hard steering, and the fifth wheel is tilted down at the rear so the trailer apron can ride up onto it.
-
27. If an intersection has two lanes marked for left turns, which one should a large vehicle use?
Show answer
Answer D: The right hand of the two turning lanes
The outside turning lane leaves room for the rear of the vehicle to swing without striking a vehicle in the adjacent lane.
-
28. Which of these is NOT on the federal list of parts and accessories the driver must be satisfied are in good working order before driving?
Show answer
Answer D: The seat cushion upholstery
The federal pre-trip rule names brakes, steering, lights and reflectors, tires, horn, wipers, mirrors, coupling devices, wheels and rims, and emergency equipment; seat upholstery is not on that list.
-
29. An article of cargo has been blocked so that it cannot move forward. How many tiedowns does the federal rule call for?
Show answer
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.
-
30. What must the driver check about the seat belt during the inspection?
Show answer
Answer A: That it is securely mounted, adjusts properly and is not ripped or frayed
A belt only restrains the driver if its anchorage is sound and the webbing is intact, so mounting and condition are both checked.
-
31. 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.
-
32. How long must a motor carrier keep a driver vehicle inspection report and the certification of repairs?
Show answer
Answer B: Three months
The original report and the certifications attached to it are kept on file for three months from the date the report was prepared.
-
33. You have chosen 40 miles per hour as your safe speed for a downgrade. How should the brakes be used?
Show answer
Answer A: Brake firmly to about 35, release, and repeat at 40
Proper technique is firm application to about 5 miles per hour below the safe speed, then full release so the brakes cool before the next application.
-
34. On a tractor with a sliding fifth wheel, what does moving the fifth wheel forward do?
Show answer
Answer A: Puts more of the trailer weight onto the steering axle
Moving the coupling point forward transfers weight from the drive axles to the steering axle, which is how a driver corrects a drive axle that is over the limit.
-
35. What is the driver looking for when the exhaust system is inspected?
Show answer
Answer B: Loose, broken or missing pipes, brackets or clamps, and signs that exhaust is leaking
A loose or leaking exhaust system can send carbon monoxide into the cab and can put hot gas against parts that will burn.
-
36. What tells you that an air suspension bag has a problem?
Show answer
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.
-
37. How should the steering wheel be held when driving a large vehicle?
Show answer
Answer D: Firmly with both hands, placed on opposite sides of the wheel
Both hands on opposite sides give the leverage and control needed if a tire drops off the pavement or the wheel is jolted.
-
38. What is wrong with resting your foot on the clutch pedal between shifts?
Show answer
Answer B: It slowly wears the clutch out, because the pressure plate is never fully engaged
Any weight on the pedal partly disengages the clutch, so it slips and wears; the foot belongs off the pedal once the shift is finished.
-
39. How much time does DC DMV allow for the CDL general knowledge test?
Show answer
Answer C: 90 minutes
DC DMV allows 90 minutes for the CDL general knowledge test and 60 minutes for each endorsement test.
-
40. An intermodal container is being carried on an ordinary flatbed rather than on a container chassis. What does that mean for securement?
Show answer
Answer B: It must be secured with tiedowns that meet the container securement requirements
A container carried on a vehicle that is not fitted with integral locking devices has to be secured to the deck with tiedowns that satisfy the rules for containers.
-
41. Which steering system findings count as defects during the inspection?
Show answer
Answer C: Bent, loose or broken column parts, arms, drag links or tie rods, and missing nuts, bolts or cotter keys
Every joint and fastener between the steering wheel and the tires carries the driver commands, so looseness or a missing retainer can end in a complete loss of steering.
-
42. Why does a load need to be balanced from side to side?
Show answer
Answer B: Because a heavy side raises the rollover risk and can overload the tires and springs on that side
An uneven load tips the balance of the vehicle in curves and pushes the tires and suspension on the loaded side past their rating.
-
43. Why are the windshield wipers on the pre-trip list even before a trip in fine weather?
Show answer
Answer C: Because weather can change and a wiper failure leaves the driver without a clear view
Rain, spray or mud can arrive at any point in a long trip, and a wiper that fails then leaves the driver with no way to clear the windshield.
-
44. How soon must warning devices be placed after a commercial vehicle stops on the traveled part or the shoulder of a highway?
Show answer
Answer D: As soon as possible and in any case within 10 minutes
The hazard warning flashers go on immediately and the warning devices must be in place as soon as possible, never later than 10 minutes after stopping.
-
45. Within what distance should high beams be lowered at night?
Show answer
Answer D: Within about 500 feet of an oncoming vehicle and within about 500 feet of a vehicle you are following
High beams blind other drivers at close range, so they are lowered at roughly the same distance whether the other vehicle is coming toward you or is ahead of you.
-
46. You are about to back across a quiet street into a driveway. Which of these is good practice before you start to move?
Show answer
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.
-
47. What blood alcohol concentration disqualifies the holder of a commercial driver license who is operating a commercial vehicle?
Show answer
Answer D: 0.04 or higher
Commercial drivers are held to 0.04, half the limit that applies to a driver of a passenger car in the same state.
-
48. You are told a posted bridge ahead has a weight limit lower than your gross weight. What must you do?
Show answer
Answer C: Take a route that avoids it, because a posted limit is a legal limit
A posted structure limit must be obeyed exactly as any other weight limit, so a heavier vehicle has to be routed around it.
-
49. 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.
-
50. How does the working load limit of a tiedown relate to the force that would break it?
Show answer
Answer B: The working load limit is a fraction of the breaking strength and is the figure you use
The working load limit is set well below the point at which the device would fail, and securement is always calculated from the working load limit, never from breaking strength.