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DC CDL General Knowledge study materials
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DC CDL General Knowledge practice questions

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Question 1Vehicle Inspection and Basic Control

During a pre-trip inspection of a Class B commercial vehicle, you check the slack adjusters on the service brakes. What should you look for?

  1. That the slack adjuster is welded to the push rod for extra strength
  2. That the slack adjuster is greased heavily so it cannot move freely
  3. That the push rod moves at least six inches before the brake applies
  4. That the push rod travel is within the limit marked on the chamber and the adjuster is not broken or loose Correct answer.

Explanation

The brake chamber push rod travel must stay within the adjustment limit marked on the chamber; too much travel means the brakes are out of adjustment and stopping distance increases. The slack adjuster must be securely mounted, not broken, and free of excessive play.

Question 2Vehicle Inspection and Basic Control

You are inspecting the engine compartment of a diesel truck before a trip. Which condition requires you to place the vehicle out of service until repaired?

  1. A slightly loose oil dipstick handle
  2. A small amount of dust on the valve cover
  3. A coolant overflow bottle filled to the hot mark
  4. A coolant hose that is cracked and seeping coolant onto hot engine parts Correct answer.

Explanation

A cracked, leaking coolant hose can fail completely and cause overheating or a fire if coolant reaches hot components, so it must be repaired before operation. Cosmetic dirt, a loose dipstick, and a properly filled overflow bottle are normal conditions.

Question 3Vehicle Inspection and Basic Control

When checking tire condition during a pre-trip inspection, which finding makes the vehicle unsafe to operate?

  1. A tread depth of 8/32 inch on the drive tires
  2. A small stone lodged in a tread groove
  3. A tire with proper cold inflation pressure
  4. A tread depth of 2/32 inch on the front steering axle tires Correct answer.

Explanation

Front steering axle tires must have at least 4/32 inch of tread depth; 2/32 inch is below that minimum and reduces traction and steering control, especially on wet roads. Drive tires require at least 2/32 inch, so 8/32 inch is fine.

Question 4Vehicle Inspection and Basic Control

During the walk-around inspection, you check the lights. Which combination should illuminate when you turn on the headlights with the engine running?

  1. Headlights and turn signal indicators on both sides steady
  2. Headlights only, with all marker lights off
  3. Headlights and backup lights
  4. Headlights, clearance lights, side marker lights, and taillights Correct answer.

Explanation

With the headlight switch on, the headlights, clearance lights, side marker lights, and taillights should all be lit so the vehicle is visible from every side at night. Backup lights come on only in reverse, and turn indicators flash only when selected.

Question 5Vehicle Inspection and Basic Control

You are about to back a tractor-trailer with a sleeper berth into a loading dock on the right side. What is the safest starting position?

  1. Position the vehicle so the trailer is angled toward the dock and back slowly using both mirrors Correct answer.
  2. Back from the left side of the roadway so the trailer swings right
  3. Back quickly to reduce the time spent in the roadway
  4. Rely on the backup alarm to warn pedestrians instead of checking mirrors

Explanation

Backing toward the right side is easier and safer when the vehicle is set up with the trailer angled toward the dock, because you can see the target in the mirrors and control the swing. Backing quickly or depending on the alarm alone removes your margin for error.

Question 6Vehicle Inspection and Basic Control

While driving a loaded tractor-trailer, you approach a curve posted with an advisory speed lower than the general limit. What should you do?

  1. Slow to the advisory speed before entering the curve and maintain a steady speed through it Correct answer.
  2. Accelerate through the curve to increase traction on the drive tires
  3. Brake hard in the middle of the curve to scrub off speed
  4. Maintain the general speed limit because the load keeps the trailer stable

Explanation

Advisory speeds account for the curve's radius and the higher center of gravity of large vehicles, so you should slow before the curve and keep a steady speed. Braking hard mid-curve or speeding up can cause a rollover or loss of control.

Question 7Vehicle Inspection and Basic Control

You are driving a straight truck on a wet road and need to stop. What is the correct braking technique?

  1. Pump the brake pedal rapidly to prevent wheel lock
  2. Shift to neutral and coast until the vehicle slows
  3. Apply the brakes only after the vehicle begins to skid
  4. Apply the brakes firmly but smoothly with both hands on the wheel and avoid locking the wheels Correct answer.

Explanation

On wet pavement, smooth firm braking keeps the wheels rolling and preserves steering control; locking the wheels causes a skid. Pumping or coasting in neutral lengthens stopping distance and reduces control.

Question 8Vehicle Inspection and Basic Control

What is the proper way to check the engine oil level on a diesel truck before a trip?

  1. By watching the oil pressure gauge only
  2. With the engine off and level, pull the dipstick, wipe it, reinsert it fully, then read the level Correct answer.
  3. With the engine running at high idle to circulate oil
  4. Immediately after shutdown while oil is still draining down

Explanation

Oil level is checked with the engine off on level ground so oil has drained back to the pan; wiping and reinserting the dipstick gives an accurate reading. Checking while running or right after shutdown gives a false low reading.

Question 9Vehicle Inspection and Basic Control

During a pre-trip inspection you find the air pressure builds from 85 to 100 psi in about 45 seconds at governed rpm with the engine at operating speed. What does this indicate?

  1. The air dryer is bypassing and must be replaced immediately
  2. The governor cut-out is set too high
  3. The air system is working normally and the vehicle may be operated
  4. The air compressor is building pressure too slowly and the system needs service Correct answer.

Explanation

A typical standard is that pressure should build from 85 to 100 psi within about 45 seconds at fast idle; taking longer indicates a weak compressor, leaks, or a restricted line that should be checked. Normal build-up is faster than this rate.

Question 10Vehicle Inspection and Basic Control

You perform the static leak test on the air brake system and find that pressure drops 4 psi in one minute with the engine off and the brakes released. What should you conclude?

  1. The gauge is faulty because air brakes never leak
  2. The leak is caused by the brake chambers and can be ignored
  3. The leak rate is normal and no action is needed
  4. The leak rate exceeds the allowable limit and the vehicle must be repaired before use Correct answer.

Explanation

With the engine off and brakes released, air loss should be no more than about 2 psi in one minute for a single vehicle; 4 psi exceeds that limit. An excessive leak must be found and repaired before the vehicle is placed in service.

Question 11Vehicle Inspection and Basic Control

When conducting the tug test before pulling out with a trailer, what are you checking?

  1. That the landing gear is fully raised
  2. That the fifth wheel jaws have locked around the kingpin and will not release under load Correct answer.
  3. That the trailer brakes hold the tractor in place
  4. That the air lines are connected in the correct order

Explanation

The tug test confirms the fifth wheel has locked onto the kingpin: with the trailer brakes set, you gently pull forward and feel the tractor resist, showing the coupling is secure. It does not test trailer brakes, landing gear position, or air line order.

Question 12Vehicle Inspection and Basic Control

You are driving a loaded tanker with a high center of gravity through a curve. Which action best reduces the risk of a rollover?

  1. Increase speed to create downforce on the tires
  2. Brake hard at the apex of the curve
  3. Reduce speed before the curve and avoid sudden steering or braking inputs Correct answer.
  4. Steer sharply to the outside to counter centrifugal force

Explanation

Rollover risk rises with speed and sudden inputs because centrifugal force and weight transfer increase. Slowing before the curve and making gentle steering and braking inputs keeps the load stable and the tires planted.

Question 13Vehicle Inspection and Basic Control

What is the correct procedure for a downshift when approaching a steep downgrade in a loaded commercial vehicle?

  1. Select a lower gear before the descent begins so engine braking controls speed Correct answer.
  2. Wait until the vehicle speeds up, then downshift
  3. Use the clutch to hold the vehicle on the grade
  4. Shift to neutral and use the service brakes to control speed

Explanation

You should be in the proper low gear before starting down a grade so engine braking helps control speed and the service brakes do not overheat. Coasting in neutral or waiting to downshift can lead to runaway speed.

Question 14Vehicle Inspection and Basic Control

During a pre-trip inspection, how should you check the steering system for excessive play?

  1. With the engine running and wheels straight ahead, turn the wheel slightly and note how far it moves before the front wheels respond Correct answer.
  2. By watching the power steering fluid level
  3. With the engine off, turn the wheel fully to each side and measure the arc
  4. By lifting the front axle off the ground and spinning the wheel

Explanation

Steering play is checked with the engine running and the wheels straight: the steering wheel should not move more than about 10 degrees (roughly two inches at the rim) before the front wheels begin to turn. Excessive play indicates worn linkage or a steering box problem.

Question 15Vehicle Inspection and Basic Control

You must make a right turn in a tractor-trailer and there is a bicyclist in the bike lane to your right. What is the safest action?

  1. Wait behind the cyclist until the turn can be completed without crossing their path Correct answer.
  2. Turn from the right lane while the cyclist passes on the left
  3. Turn wide to the left and accelerate through the turn
  4. Sound the horn and proceed with the turn

Explanation

Large vehicles swing wide on right turns and have blind spots on the right side, so turning across a cyclist's path risks a side-swipe or crush. Waiting until the cyclist clears the area lets you complete the turn safely.

Question 16Vehicle Inspection and Basic Control

What is the correct way to use the trailer hand valve (trolley valve) while driving?

  1. It should not be used for parking or normal braking; it is only for testing trailer brakes Correct answer.
  2. It should be used for all normal stops to save tractor brakes
  3. It should be left partially applied to improve trailer stability
  4. It should be used to hold the vehicle on a hill

Explanation

The trailer hand valve applies only the trailer brakes and is intended for testing the trailer brake system, not for parking or routine stopping. Using it while driving can cause a jackknife or leave the trailer brakes dragging.

Question 17Vehicle Inspection and Basic Control

You are inspecting the coupling system and notice the locking jaws on the fifth wheel are not completely closed around the kingpin. What should you do?

  1. Apply the trailer brakes and pull forward to force the jaws closed
  2. Proceed slowly and let the weight of the trailer seat the jaws
  3. Do not move the vehicle until the jaws are fully closed and locked Correct answer.
  4. Lower the landing gear and drive away

Explanation

If the jaws are not fully closed around the kingpin, the trailer can separate from the tractor, causing a serious crash. The coupling must be corrected and rechecked with a tug test before the vehicle moves.

Question 18Vehicle Inspection and Basic Control

You are driving at highway speed when the trailer begins to sway side to side. What is the correct response?

  1. Steer sharply in the opposite direction of the sway
  2. Accelerate to pull the trailer straight
  3. Brake firmly to stop the sway
  4. Ease off the accelerator and steer straight without braking hard Correct answer.

Explanation

Trailer sway is corrected by reducing speed gradually and holding the steering wheel steady so the trailer settles; hard braking or sharp steering can amplify the sway and cause a jackknife. Accelerating increases the oscillation.

Question 19Vehicle Inspection and Basic Control

When should you use the parking (spring) brakes on a commercial vehicle?

  1. Whenever the vehicle is parked, because they apply automatically when air pressure is lost Correct answer.
  2. Only when the engine is running
  3. Only when parking on a level surface
  4. Only when the trailer is disconnected

Explanation

Spring brakes are held applied by heavy springs and release only when air pressure builds, so they set automatically if air pressure is lost. They should be used whenever the vehicle is parked, on any grade, as the primary parking brake.

Question 20Vehicle Inspection and Basic Control

During your pre-trip inspection, you check the exhaust system. Which condition is a defect that must be repaired?

  1. A rusted-through hole in the exhaust pipe under the cab Correct answer.
  2. An exhaust hanger that is tight and unbroken
  3. A heat shield that is securely fastened
  4. A slight discoloration on the muffler surface

Explanation

A hole in the exhaust system allows carbon monoxide and hot gases to enter the cab or reach combustible materials, creating a poisoning and fire hazard. It must be repaired before the vehicle is operated.

Question 21Vehicle Inspection and Basic Control

You are preparing to drive a vehicle with a manual transmission on a steep uphill grade. What technique helps prevent rolling backward?

  1. Shift to a higher gear before releasing the brake
  2. Engage the parking brake, release it as the clutch engages and the vehicle begins to move Correct answer.
  3. Hold the vehicle with the clutch on the grade
  4. Release the clutch quickly while the brake is still applied

Explanation

Using the parking brake to hold the vehicle while you engage the clutch and add power prevents rollback until the drivetrain takes the load. Holding the vehicle with the clutch or releasing it abruptly causes wear and stalling.

Question 22Vehicle Inspection and Basic Control

What is the purpose of the pre-trip inspection report required of commercial drivers?

  1. To certify that the driver holds a valid medical card
  2. To list the cargo weight and axle loads
  3. To record the driver's hours of service for the day
  4. To document defects found and ensure they are repaired before the vehicle is operated Correct answer.

Explanation

The pre-trip inspection report records any defects discovered so the carrier can have them repaired and the driver can certify the vehicle is safe to operate. It does not serve as an hours-of-service log, weight record, or medical certification.

Question 23Vehicle Inspection and Basic Control

You are driving a bus and must stop at a railroad crossing. Which action is required before proceeding?

  1. Stop, open the door or window, look and listen for a train, then proceed when clear Correct answer.
  2. Stop only if a train is visible
  3. Slow down and proceed without stopping if the crossing has no gates
  4. Sound the horn and drive across without stopping

Explanation

Buses carrying passengers must stop at railroad crossings, open the door or window to look and listen, and proceed only when the tracks are clear. Slowing without stopping or relying on sight alone is not sufficient.

Question 24Vehicle Inspection and Basic Control

When checking the mirrors before a trip, what adjustment should you make on the flat side mirrors?

  1. Adjust them to show the trailer wheels only
  2. Point them inward so the driver's face is visible
  3. Set them so you can see a portion of the vehicle side and the traffic lane behind Correct answer.
  4. Aim them so they show only the sky and horizon

Explanation

Flat side mirrors should be adjusted to show a small part of the vehicle side and the lane behind so you can monitor traffic and clearances. Aiming them at the sky or at the driver wastes the mirror's field of view.

Question 25Shifting, Backing, and Turning

Before backing a heavy combination vehicle, what is the safest first step?

  1. Accelerate slightly to overcome rolling resistance
  2. Sound the horn twice and rely on the mirrors
  3. Turn the steering wheel fully to the left before reversing
  4. Get out and walk around the vehicle to check for obstacles and clearance Correct answer.

Explanation

A walk-around inspection before reversing reveals obstacles, pedestrians, low clearances, and hazards that mirrors cannot show, especially directly behind a trailer. It is the standard first step in safe backing procedure and must be done before any wheel movement.

Question 26Shifting, Backing, and Turning

When backing a tractor-trailer, which mirror position gives the best view of the rear of the trailer?

  1. The hood-mounted crossover mirror
  2. The flat left mirror only
  3. The interior rearview mirror
  4. The convex spot mirror on the side the trailer is being turned toward Correct answer.

Explanation

Convex spot mirrors widen the field of view along the side and rear of the trailer, so they show the trailer's rear corner during a turn better than flat mirrors. The driver should watch the spot mirror on the side the trailer is being pushed toward.

Question 27Shifting, Backing, and Turning

Which statement correctly describes the path of a large commercial vehicle making a right turn?

  1. The rear wheels follow exactly in the tracks of the front wheels
  2. The rear wheels track inside the path of the front wheels, so the vehicle sweeps toward the inside of the turn Correct answer.
  3. The trailer tracks wider than the tractor on every turn
  4. The rear wheels swing outward, away from the curb

Explanation

Because the rear wheels of a long vehicle cut inside the arc traced by the front wheels, the vehicle needs extra room on the inside of a right turn. This off-tracking is why trucks often swing left before turning right and why curbs and poles are struck.

Question 28Shifting, Backing, and Turning

A driver must back a tractor-trailer around a corner to the left. Which technique is correct?

  1. Back toward the driver's side so the trailer is visible in the left mirror Correct answer.
  2. Back straight with both mirrors covered by the load
  3. Back toward the passenger side to keep the trailer in the right mirror
  4. Back quickly to reduce the time spent in the roadway

Explanation

Backing toward the driver's side keeps the trailer visible in the left mirror and allows a more controlled correction of steering. Turning toward the blind passenger side is far harder to monitor and is avoided when a choice exists.

Question 29Shifting, Backing, and Turning

Why should a driver pull forward after completing a backing maneuver rather than stopping abruptly?

  1. To cool the brakes
  2. To straighten the combination and clear the travel lane Correct answer.
  3. To re-engage the interaxle differential
  4. To reset the trailer air supply

Explanation

Pulling forward after backing straightens the tractor and trailer, centers the unit in the space, and clears the lane for other traffic. Abrupt stopping while still angled can leave the trailer obstructing the roadway.

Question 30Shifting, Backing, and Turning

When making a left turn in a large truck, why should the driver begin the turn from the right side of the lane?

  1. To keep the rear wheels from crossing the centerline or striking the left curb Correct answer.
  2. To shorten the turning radius
  3. To increase engine rpm for the turn
  4. To allow the trailer to swing into the right lane

Explanation

Starting a left turn from the right side of the lane allows the rear wheels to clear the left curb and keeps the vehicle from crossing the centerline. It compensates for off-tracking on the inside of the turn.

Question 31Shifting, Backing, and Turning

Which situation makes a right turn especially risky for a tractor-trailer?

  1. A downhill grade after the turn
  2. A wide shoulder on the right side
  3. A green light with no cross traffic
  4. A pedestrian standing on the corner inside the turn path Correct answer.

Explanation

Because the rear wheels and trailer cut inside the turn, a pedestrian on the corner can be struck even though the cab cleared them. Drivers must check the inside of the turn for people, cyclists, and objects before and during the turn.

Question 32Shifting, Backing, and Turning

A driver is backing a trailer that begins to drift off line. What is the correct correction?

  1. Apply the trailer hand valve to straighten the trailer
  2. Steer the top of the steering wheel toward the direction the trailer should go Correct answer.
  3. Steer the top of the steering wheel away from the direction the trailer should go
  4. Hold the wheel steady and continue backing

Explanation

When backing, steering the top of the wheel toward the side you want the trailer to move corrects the drift. Steering opposite the desired direction worsens the jackknife angle.

Question 33Shifting, Backing, and Turning

What should a driver do if visibility behind the vehicle is poor and no spotter is available?

  1. Back faster to reduce exposure time
  2. Get out and recheck the path, then back only as far as can be seen clearly Correct answer.
  3. Rely on the backup alarm to clear the area
  4. Use the horn continuously while backing

Explanation

If the driver cannot see the path clearly, backing must stop until the area is verified. Getting out to recheck or using a spotter are the accepted remedies; alarms and horns do not guarantee the area is clear.

Question 34Shifting, Backing, and Turning

Which of these is a correct use of a spotter while backing?

  1. Have the spotter stand directly behind the trailer
  2. Have the spotter walk backward in front of the cab
  3. Agree on hand signals and keep the spotter in view in the mirror Correct answer.
  4. Rely on the spotter to stop traffic in all directions

Explanation

A spotter should be positioned where the driver can see them in the mirror, and hand signals should be agreed on before backing begins. The driver remains responsible for stopping if the spotter disappears from view.

Question 35Shifting, Backing, and Turning

What is the main reason a truck driver swings wide before a turn?

  1. To engage the differential lock
  2. To allow following vehicles to pass on the inside
  3. To increase the vehicle's speed through the turn
  4. To keep the rear wheels from running over the curb or crossing the centerline Correct answer.

Explanation

Swinging wide compensates for off-tracking so the rear wheels clear the curb on a right turn or the centerline on a left turn. It must be done without crowding other lanes or traffic.

Question 36Shifting, Backing, and Turning

A driver must turn a long combination vehicle in a tight space. Which approach is best?

  1. Make the turn in one smooth, wide arc using all available space Correct answer.
  2. Make several short back-and-forth corrections in the intersection
  3. Stop in the intersection and reassess after the light changes
  4. Turn sharply and let the trailer follow

Explanation

A single smooth, wide arc uses the available space and keeps the trailer clear of curbs and opposing traffic. Multiple corrections in an intersection increase exposure and risk.

Question 37Shifting, Backing, and Turning

During a backing maneuver, why should the driver use the lowest reverse gear or reverse range?

  1. To increase engine braking on the trailer
  2. To reduce fuel consumption
  3. To prevent the trailer brakes from engaging
  4. To keep speed low and allow time to react and correct Correct answer.

Explanation

Backing should be done at a crawl so the driver has time to see hazards and correct steering errors. A low range limits speed and improves control.

Question 38Shifting, Backing, and Turning

What is the correct response if a driver loses sight of the spotter during a backing maneuver?

  1. Stop immediately until the spotter is visible again Correct answer.
  2. Assume the spotter has cleared the path
  3. Sound the horn and keep backing
  4. Continue slowly using the mirrors

Explanation

The spotter's visibility is the driver's assurance that the path is clear. If the spotter disappears from view, the driver must stop until contact is re-established.

Question 39Shifting, Backing, and Turning

Which factor most increases the off-tracking of a combination vehicle?

  1. A lighter payload
  2. A larger fuel tank
  3. A longer wheelbase and a longer trailer Correct answer.
  4. A higher axle ratio

Explanation

Off-tracking grows with the distance between the front axle and the rear axles and with trailer length. Longer wheelbases and longer trailers therefore cut a tighter inside path and need more room.

Question 40Shifting, Backing, and Turning

When backing a straight truck with no trailer, which practice improves safety?

  1. Rely only on the left mirror
  2. Back until the backup alarm stops sounding
  3. Back with the driver's door open for a better view
  4. Use both mirrors and check the area behind before moving Correct answer.

Explanation

A straight truck has blind spots behind the body, so the driver should check the area behind before moving and use both mirrors while backing. Backing with the door open is unsafe and the alarm is a warning, not a guide.

Question 41Seeing Hazards and Space Management

When driving a commercial vehicle, the distance your vehicle travels between the moment you see a hazard and the moment you begin to brake is called:

  1. Following distance
  2. Perception distance
  3. Reaction distance Correct answer.
  4. Braking distance

Explanation

Reaction distance is the ground covered during the time it takes to move your foot to the brake after recognizing a hazard. Perception distance is the travel before you recognize it, and braking distance is the travel after the brakes engage. Total stopping distance combines perception, reaction, and braking distance.

Question 42Seeing Hazards and Space Management

A school bus ahead of you on a two-lane road activates its flashing red lights. What does safe space management require you to do?

  1. Stop and remain stopped until the red lights stop flashing Correct answer.
  2. Move to the shoulder and continue past the bus
  3. Pass quickly before children reach the roadway
  4. Slow to 25 mph and proceed with caution

Explanation

Flashing red lights on a school bus mean children are loading or unloading, so you must stop and stay stopped until the lights are turned off. Passing during red lights endangers children who may cross in front of or behind the bus. Only on a divided highway with a physical median do opposite-direction drivers have different obligations.

Question 43Seeing Hazards and Space Management

You are driving a tractor-trailer and want to follow the vehicle ahead at a safe distance. The recommended minimum following time under ideal conditions is:

  1. One second regardless of speed
  2. Four seconds at all speeds
  3. One second for each ten feet of vehicle length Correct answer.
  4. Two seconds at all speeds

Explanation

The standard guidance is one second of following distance for each ten feet of vehicle length at speeds below 40 mph, with an extra second added above 40 mph. A 60-foot combination vehicle therefore needs about six seconds at low speed and seven at highway speed. Fixed seconds-at-all-speeds rules ignore how much longer heavy vehicles take to stop.

Question 44Seeing Hazards and Space Management

While scanning the road ahead, you notice a driver in a side street looking down at a phone rather than at the intersection. The best space-management response is to:

  1. Sound your horn and maintain your speed and lane
  2. Flash your headlights and stay in the same position
  3. Cover the brake, reduce speed, and be ready to change lanes or stop Correct answer.
  4. Assume the driver will look up before entering and continue

Explanation

A distracted driver who has not looked toward your lane is a developing hazard, so you should create time and space by slowing and preparing to stop or move over. Reducing speed buys the seconds needed if the driver pulls out. Horn or light flashes only help once the other driver is looking.

Question 45Seeing Hazards and Space Management

Which of these is a clue that a driver ahead may be about to make a sudden move?

  1. The driver is holding a steady speed in the center of the lane
  2. The driver is using a turn signal well in advance
  3. The driver keeps glancing in the mirror and drifting within the lane Correct answer.
  4. The driver is maintaining a large following distance

Explanation

Drifting within the lane combined with repeated mirror checks suggests the driver is distracted, uncertain, or preparing to change lanes. Such behavior warns you to drop back and give room. Steady lane position and early signaling are signs of predictable driving.

Question 46Seeing Hazards and Space Management

You are descending a long mountain grade and notice your speed climbing despite being in a lower gear. What should you do?

  1. Coast in neutral to let the engine cool
  2. Ride the brakes lightly and continuously
  3. Shift to a lower gear and use the brakes firmly to bring speed down Correct answer.
  4. Accelerate to build momentum through the grade

Explanation

On a downgrade you should select a gear low enough to control speed and use firm, short brake applications to reduce speed before it builds. Continuous light braking overheats the brakes and causes fade. Coasting in neutral removes engine braking and is unsafe and often illegal.

Question 47Seeing Hazards and Space Management

Your combination vehicle is 70 feet long. Under ideal conditions at speeds above 40 mph, the recommended following time is about:

  1. Five seconds
  2. Eight seconds Correct answer.
  3. Six seconds
  4. Seven seconds

Explanation

The rule is one second per ten feet of vehicle length, plus one extra second when traveling above 40 mph. A 70-foot vehicle therefore needs seven seconds for length plus one, for about eight seconds. This gap gives you room to stop if the vehicle ahead brakes suddenly.

Question 48Seeing Hazards and Space Management

When you approach the crest of a hill, why should you reduce speed and stay to the right side of your lane?

  1. Because engine power decreases at higher elevations
  2. Because you cannot see oncoming traffic or obstacles beyond the crest Correct answer.
  3. To improve fuel economy on the climb
  4. To allow faster vehicles to pass on the left shoulder

Explanation

The crest of a hill blocks your view of the road beyond, so an oncoming vehicle, stopped traffic, or debris may be hidden until it is too late. Slowing and staying right gives you more time and room to react. The problem is limited sight distance, not fuel economy or engine power.

Question 49Seeing Hazards and Space Management

You are driving at night and a vehicle approaching from the opposite direction keeps its high beams on. To manage the glare, you should:

  1. Speed up to get past the vehicle quickly
  2. Stare directly at the headlights to judge the vehicle's position
  3. Turn on your own high beams until the vehicle passes
  4. Look toward the right edge of your lane and slow down Correct answer.

Explanation

Looking toward the right edge of your lane keeps you centered while avoiding the glare of oncoming high beams. Slowing down gives you more time to react while your vision is reduced. Staring at the lights or retaliating with high beams worsens the glare problem.

Question 50Seeing Hazards and Space Management

Which condition should you treat as requiring a larger safety cushion around your commercial vehicle?

  1. A smooth, dry road surface
  2. Rain, snow, or icy pavement Correct answer.
  3. Light traffic on an open highway
  4. Clear weather with good visibility

Explanation

Wet, snowy, or icy pavement reduces traction and lengthens stopping distance, so you need more space around the vehicle. The general guidance is to add following time in poor conditions, often doubling it. Dry roads and light traffic do not require the same extra margin.