District of Columbia DC DMV CDL General Knowledge Practice Test 5
Test 5 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 District of Columbia test.
- Questions50
- Correct to pass40
- Passing score80%
- Minimum age18 years
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1. A commercial driver is convicted of two serious traffic violations within three years. What is the result?
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Answer D: Disqualification for 60 days
Two serious traffic violations in a three year period bring a 60 day disqualification, and a third in the same period raises it to 120 days.
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2. Where should a trailer be dropped, and what else does the driver do before pulling out from under it?
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Answer C: On solid level ground, with the trailer wheels chocked if it may roll
A dropped trailer must sit on ground that will carry the landing gear without sinking, and chocks stop it rolling once the tractor and its air supply are gone.
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3. As a long vehicle goes around a corner, how do the rear wheels travel compared with the front wheels?
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Answer A: They follow a tighter path, closer to the inside of the turn
The rear wheels off-track toward the inside of the turn, and the longer the vehicle the bigger the difference, which is why the front must swing wide enough to keep the rear off the curb.
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4. What is the correct way to make a right turn in a long vehicle?
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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.
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5. Why should both outside mirrors be checked over and over while backing?
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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.
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6. What speed and gear should be used when backing a large vehicle?
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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.
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7. What does the suspension system weight rating tell the driver?
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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.
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8. 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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9. Besides the hours when the law requires them, when should headlights be switched on?
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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.
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10. Regular mirror checks during a long trip can reveal which developing problem?
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Answer D: Smoke coming from a tire or from a wheel
Overheating tires, wheel bearings and brakes usually show as smoke long before anything appears on the dash, and mirrors are where a driver sees it.
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11. Within total stopping distance, what exactly is perception distance?
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Answer D: The distance traveled from the moment your eyes see a hazard until your brain identifies it
Perception distance covers only the time between seeing a hazard and recognizing it as a hazard, before any physical reaction begins.
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12. Why should water never be used on an electrical fire or a gasoline fire?
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Answer C: It spreads the fuel and conducts the current
Water carries current back to the person holding the hose and floats burning fuel outward, which is why a B:C rated extinguisher is carried instead.
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13. 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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14. What is generally the safest speed in dense but freely moving highway traffic?
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Answer D: The speed of the traffic around you, up to the posted limit
Crashes rise with the difference between your speed and the traffic around you, so moving with the flow within the legal limit is safest.
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15. A hard frost has left your vehicle covered in ice. What must be cleared before you drive?
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Answer D: The windshield, mirrors, lights and reflectors
You must be able to see out and other drivers must be able to see your lights and reflectors, so all of those surfaces have to be cleared.
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16. Why must a bent, cracked or badly seated lock ring be reported?
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Answer D: It can come off under pressure and let the tire and rim separate violently
The lock ring holds the assembly together against the full pressure of the tire, so a damaged ring can release with enough force to kill.
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17. What are you looking for when you check the hubs and wheel seals during the walkaround?
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Answer B: Leaking oil or grease, which can also contaminate the brake linings
A leaking hub seal starves the bearing of lubricant and the escaping oil or grease can soak the brake linings and cut braking power.
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18. Under the federal hours of service rules, how long may a property-carrying driver drive after 10 consecutive hours off duty?
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Answer D: Up to 11 hours, and only within a 14 hour window that starts when the driver comes on duty
The federal limit is 11 hours of driving after 10 consecutive hours off duty, and all of that driving has to fall inside a 14 hour window.
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19. 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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20. What is the minimum age for a DC commercial driver license used to drive across state lines?
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Answer D: 21
Interstate commercial driving from the District requires the applicant to be at least 21 and to hold a valid non-commercial license.
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21. An automatic transmission is left in its normal drive position as the vehicle rolls down a long grade. What does it tend to do?
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Answer A: Shift up as road speed rises, so engine braking falls away
An automatic left in drive keeps upshifting as speed builds, which is the opposite of what you want on a grade; that is why the driver must select a low range.
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22. Why should a driver avoid stopping partway up a snow covered hill?
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Answer D: You may not get moving again and could slide backwards
On a slippery grade the drive wheels may simply spin when you try to restart, leaving the vehicle stuck across the road or sliding back down it.
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23. You are on a freeway and see brake lights come on in several vehicles far ahead of you. What should you do?
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Answer A: Ease off the accelerator and get ready to slow down
Brake lights well ahead are an early warning that traffic is slowing, and acting on them gives a heavy vehicle the room it needs.
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24. While double clutching, what goes wrong if you take too long between the two clutch movements?
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Answer A: Engine speed falls too far and the gear becomes hard or impossible to engage
Double clutching only works while engine speed and road speed still match; a slow shift lets rpm drop away and the gear will not go in.
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25. What should you check about the fuel tank during the walkaround?
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Answer A: That it is securely mounted, the cap is on tight and there are no leaks
A loose tank or a missing cap can spill fuel, and any fuel leak is a fire hazard that makes the vehicle unsafe to drive.
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26. How does the working load limit of a tiedown relate to the force that would break it?
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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.
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27. Which vehicle condition makes hydroplaning more likely?
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Answer C: Tires that are worn or underinflated
Tread depth and correct pressure are what let a tire push water aside, so worn or soft tires lift onto the water film at lower speeds.
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28. What extinguisher rating is required on a vehicle carrying hazardous materials in amounts that need placards?
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Answer B: 10 B:C or more
Placarded loads carry a much higher fire risk, so the required extinguisher rating rises to at least 10 B:C.
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29. Why must you never coast down a hill in neutral or with the clutch pushed in?
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Answer C: You lose the braking effect of the engine and your brakes may overheat and fail
Engine braking is what keeps a heavy vehicle in check on a grade; coasting throws it away and leaves the service brakes to do all the work until they overheat.
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30. What happens when too much of the load sits over the steering axle?
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Answer D: The vehicle becomes hard to steer and the axle and its tires can be damaged
Weight beyond the front axle rating makes the steering heavy and can overload the axle and the tires carrying it.
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31. What can repeated violations of the federal phone and texting rules cost a commercial driver?
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Answer D: Disqualification of the commercial driver license
Multiple convictions for using a hand-held phone or texting while driving a commercial vehicle lead to disqualification, on top of fines for driver and carrier.
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32. You are taking a tightly curved highway exit ramp in a long combination. Where should the tractor be placed within the lane?
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Answer D: Toward the outside of the curve, leaving room for the trailer to track inside
Because the trailer wheels cut to the inside of the curve, the tractor has to be kept out toward the outer edge so the trailer does not drop a wheel off the inside edge.
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33. What is the purpose of the header board, or headache rack, that you inspect behind the cab?
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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.
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34. You need fuel and the canopy over the pumps is low. What is the safe way to handle the clearance?
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Answer B: Stop and check the height at the entrance and at the way out before committing
Clearance can differ at the entry, under the canopy and at the exit, and a sloping approach changes the effective height, so both ends have to be checked.
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35. 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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36. Which road users are hardest to see at night?
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Answer C: Pedestrians and cyclists in dark clothing
People on foot or on a bicycle carry no lights of their own in many cases, so they appear only when the headlights reach them.
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37. Most rollovers of loaded trucks on exit and entrance ramps happen for which reason?
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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.
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38. 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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39. In hazard perception, what counts as a hazard?
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Answer C: Any road user or condition that could become a danger
A hazard is anything with the potential to create danger, which is why drivers are taught to spot them early rather than react to emergencies.
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40. Which document must be available to show that the annual inspection was carried out?
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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.
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41. Your windshield washer reservoir is empty and rain and road spray are expected. What should you do?
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Answer D: Fill it before the trip, because you need the washers to keep the windshield clear
Wipers alone smear the film of oil and grit thrown up by traffic, so the washers are part of keeping a usable view of the road.
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42. How are the extra gears of a multi-speed rear axle or auxiliary transmission usually controlled?
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Answer D: With a selector knob or switch on the gearshift lever of the main transmission
A range selector on the shift lever lets the driver choose the extra gear range while shifting the main transmission.
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43. 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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44. How much sleep does a typical adult driver need each day to stay properly alert?
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Answer D: Seven to eight hours
Most adults need seven to eight hours of sleep in every 24 hours, and a driver who regularly gets less builds up a debt that shows up behind the wheel.
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45. Does the federal texting ban apply to a company dispatching device mounted in the cab?
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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.
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46. Within what distance should high beams be lowered at night?
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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.
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47. Why should the mirrors be checked repeatedly while you make a tight turn?
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Answer C: To watch the rear of the vehicle clear other vehicles and objects
In a long vehicle the rear wheels cut inside the path of the front wheels, so only the mirrors show whether the rear is clearing curbs, poles and other vehicles.
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48. A vehicle becomes unsafe while you are already on the road. What does the federal rule allow?
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Answer A: Continuing only to the nearest place where repairs can safely be made
If stopping where you are would be more dangerous than moving, the rule allows you to reach the nearest place where the vehicle can safely be repaired, and no further.
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49. 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?
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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.
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50. Which brake lining condition must be reported?
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Answer C: Linings that are worn thin, loose, cracked or soaked with oil or grease
Linings must have enough material left and must be securely attached and clean, because a thin, loose or contaminated lining cannot deliver its share of braking.