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Missouri CDL General Knowledge study materials
Missouri CDL General Knowledge study resources

Missouri CDL General Knowledge practice questions

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Question 1Vehicle Inspection and Basic Control

During a pre-trip inspection, you check the slack adjusters on a vehicle with automatic slack adjusters. Which condition indicates a problem that must be corrected before driving?

  1. The push rod and slack adjuster sit at roughly a 90-degree angle
  2. The brake chamber has a light film of dust on the housing
  3. The slack adjuster moves freely when the brake is released
  4. The push rod stroke exceeds the adjustment limit for the chamber size Correct answer.

Explanation

Automatic slack adjusters should keep push rod stroke within the limit stamped for the chamber size. If the stroke is too long, the brake may not apply fully and the vehicle is out of service until repaired. Free movement at release and a near-90-degree angle are normal conditions.

Question 2Vehicle Inspection and Basic Control

When performing the air brake leakage test on a single vehicle, what is the maximum allowable pressure loss with the engine off and the brakes fully applied?

  1. 3 psi in one minute Correct answer.
  2. 5 psi in one minute
  3. 1 psi in one minute
  4. 10 psi in one minute

Explanation

With a fully charged system, the engine off, and the service brake held fully applied, leakage should not exceed 3 psi in one minute for a single vehicle. A larger drop means air is escaping and the system needs repair before operation.

Question 3Vehicle Inspection and Basic Control

While inspecting a trailer, you find the air lines are crossed between the tractor and trailer. What is the expected result when you release the parking brakes?

  1. The trailer brakes will stay applied or release at the wrong time Correct answer.
  2. Only the tractor brakes will be affected by the crossed lines
  3. The trailer brakes will operate exactly as designed
  4. The trailer lights will fail whenever the brakes are applied

Explanation

Crossed service and emergency lines can keep trailer brakes applied or make them release out of sequence with the tractor. This is a serious defect that must be corrected before the combination is moved. Properly connected lines let the trailer brakes apply and release with the tractor.

Question 4Vehicle Inspection and Basic Control

You are checking the coupling system after connecting a tractor to a semitrailer. Which observation confirms the fifth wheel is properly locked?

  1. A firm pull with the tractor in low gear does not separate the units Correct answer.
  2. The trailer landing gear still touches the ground
  3. The kingpin can be seen resting above the fifth wheel plate
  4. The release handle is pulled out with the safety latch open

Explanation

A tug test in low gear with the trailer brakes set confirms the kingpin is captured by the locking jaws. If the tractor pulls free or the handle is not seated, the coupling is not secure. The release handle should be pushed in with the safety latch closed.

Question 5Vehicle Inspection and Basic Control

What is the correct way to test the service brakes during a pre-trip inspection?

  1. Pump the brake pedal rapidly with the engine off
  2. Release the parking brake, move slowly forward, and apply the brake pedal Correct answer.
  3. Apply the trailer hand valve while parked
  4. Set the parking brake and press the accelerator

Explanation

A service brake test is done by releasing the parking brake, moving the vehicle slowly forward, and applying the foot brake to confirm it stops the vehicle. The parking brake test is a separate check. Testing while parked or with the hand valve does not verify the service brakes stop a moving vehicle.

Question 6Vehicle Inspection and Basic Control

During the walk-around inspection, which tire condition requires the vehicle to be placed out of service?

  1. A rear tire with 6/32 inch of tread depth
  2. A tire with a small stone in the tread groove
  3. A front tire with a deep cut exposing the fabric cord Correct answer.
  4. A tire with a valve cap missing on one stem

Explanation

Any cut or damage on a steering axle tire that exposes cord material makes the vehicle unsafe and out of service. Tread depth of 6/32 inch on a rear tire is above the minimum. A trapped stone or missing valve cap is minor and does not by itself require removal from service.

Question 7Vehicle Inspection and Basic Control

How should you adjust the seat before beginning a trip?

  1. So your knees are locked straight when pressing the brake
  2. So you sit as far back as possible for maximum legroom
  3. So your arms are fully extended to reach the top of the wheel
  4. So you can fully depress the clutch and reach the pedals while seeing the mirrors Correct answer.

Explanation

The seat should allow full pedal travel, including the clutch, while you can still see the mirrors and reach the controls comfortably. Sitting too far back or with locked knees reduces control and braking force. Arms should be slightly bent, not fully extended.

Question 8Vehicle Inspection and Basic Control

You must back a large combination vehicle into a loading dock on the driver's side. What is the safest procedure?

  1. Use a helper as a spotter and back slowly using both mirrors Correct answer.
  2. Sound the horn continuously and back without stopping
  3. Rely only on the backup camera and skip the mirrors
  4. Back quickly to reduce time in the roadway

Explanation

Backing a large vehicle should be done slowly with a spotter whenever possible, using both mirrors to monitor the path. Speed reduces your reaction time and increases the chance of a collision. Cameras supplement but do not replace mirror checks and a spotter.

Question 9Vehicle Inspection and Basic Control

When making a right turn in a large vehicle, why should you swing wide to the left before the turn?

  1. To signal other drivers that you are turning right
  2. To shorten the distance the trailer travels through the turn
  3. To allow faster acceleration out of the turn
  4. To keep the rear wheels from running over the curb or a nearby object Correct answer.

Explanation

Large vehicles off-track, meaning the rear wheels follow a shorter path than the front wheels. Swinging wide before a right turn keeps the rear tires and trailer from striking the curb or objects at the corner. It does not shorten the turn or replace turn signals.

Question 10Vehicle Inspection and Basic Control

What is the proper hand position when turning the steering wheel of a heavy truck?

  1. Both hands on the wheel, using a push-pull motion Correct answer.
  2. One hand resting on the gear shift lever
  3. Palms open with fingers inside the wheel spokes
  4. One hand at the top of the wheel at all times

Explanation

Keeping both hands on the wheel and using a push-pull motion gives the best control and reduces the chance of injury from the wheel spinning back. Placing hands inside the spokes or one hand on the wheel risks a broken arm or loss of control.

Question 11Vehicle Inspection and Basic Control

You are driving a loaded tractor-trailer on a downgrade and the speed begins to climb above a safe level. What is the correct action?

  1. Shift to neutral to coast and save fuel
  2. Accelerate to clear the hill faster
  3. Hold the clutch in and ride the brakes continuously
  4. Select a lower gear before the speed rises too high and use the brakes sparingly Correct answer.

Explanation

On a downgrade you should choose a gear that holds a safe speed before the vehicle gains too much speed, then use the brakes lightly to control it. Coasting in neutral or holding the clutch in removes engine braking and is dangerous. Continuous hard braking can overheat the brakes and cause fade.

Question 12Vehicle Inspection and Basic Control

When driving through a curve, when should you reduce your speed?

  1. At the midpoint of the curve
  2. After the front wheels are in the curve
  3. After you exit the curve
  4. Before entering the curve Correct answer.

Explanation

Speed should be reduced before entering a curve so the vehicle stays in its lane without hard braking mid-turn. Braking or accelerating sharply inside a curve can cause a skid or a rollover, especially with a high center of gravity.

Question 13Vehicle Inspection and Basic Control

What is the proper way to check the engine compartment during a pre-trip inspection?

  1. Check the oil level immediately after shutting off a hot engine
  2. Open the coolant cap while the engine is hot to check the level
  3. Leave the engine running and reach into the fan area
  4. Check fluid levels, belts, hoses, and look for leaks with the engine off Correct answer.

Explanation

Engine compartment checks are done with the engine off, looking at fluid levels, belt condition, hose condition, and signs of leaks. Opening a hot coolant cap can cause severe burns from scalding fluid. Reaching near a running fan or belt risks serious injury.

Question 14Vehicle Inspection and Basic Control

During a pre-trip inspection you find the power steering fluid is low and there is a visible leak. What should you do?

  1. Ignore the leak because power steering is not required for control
  2. Do not drive the vehicle until the leak is repaired and the fluid is at the proper level Correct answer.
  3. Add fluid and drive, checking the level again at the next stop
  4. Drain the remaining fluid to prevent further leakage

Explanation

A power steering leak can cause loss of steering assist while driving, so the vehicle should not be operated until it is repaired. Simply topping off fluid does not fix the leak and may fail again on the road. Power steering is needed for safe control of a heavy vehicle.

Question 15Vehicle Inspection and Basic Control

What should you check about the exhaust system during a pre-trip inspection?

  1. That it is secure, undamaged, and not leaking into the cab Correct answer.
  2. That it is painted a bright color
  3. That the muffler is the largest component on the vehicle
  4. That the tailpipe points straight up

Explanation

The exhaust system must be secure and free of cracks or leaks, especially any leak that could allow carbon monoxide into the cab. Loose or damaged exhaust parts are a safety and out-of-service concern. Color, size, and pipe direction are not inspection criteria.

Question 16Vehicle Inspection and Basic Control

You are inspecting the lights on a combination vehicle before a night trip. Which check is required?

  1. Confirm clearance lights, headlights, turn signals, and brake lights all work Correct answer.
  2. Check only the headlights since the rest are optional
  3. Verify that the trailer marker lights are disconnected
  4. Test the lights with the battery disconnected

Explanation

All required lighting, including clearance lights, headlights, turn signals, and brake lights, must function before driving. Clearance and marker lights help other drivers see the vehicle's size at night. Lights cannot be tested with the battery disconnected.

Question 17Vehicle Inspection and Basic Control

What does the term 'off-tracking' mean when describing a large vehicle in a turn?

  1. The trailer brakes apply later than the tractor brakes
  2. The front wheels drift outward while the rear wheels stay on line
  3. The vehicle's speed increases through the curve
  4. The rear wheels follow a path closer to the inside of the turn than the front wheels Correct answer.

Explanation

Off-tracking describes how the rear wheels of a long vehicle cut the corner and travel a shorter path than the front wheels. Drivers must allow for this by swinging wide and watching the rear in mirrors. It is a geometry effect, not a braking or speed issue.

Question 18Vehicle Inspection and Basic Control

While driving, you notice the steering feels loose and the vehicle wanders in its lane. What is the safest response?

  1. Increase speed to stabilize the vehicle
  2. Ignore it if the road is straight
  3. Slow down, pull off safely, and inspect the steering before continuing Correct answer.
  4. Continue at highway speed and monitor the condition

Explanation

Loose steering or wandering indicates a possible steering defect that can worsen and cause loss of control. The safe response is to slow down, stop in a safe place, and inspect or get repairs before continuing. Speeding up or ignoring the symptom increases crash risk.

Question 19Vehicle Inspection and Basic Control

What is the purpose of the tug test during coupling?

  1. To check the trailer lights are connected
  2. To confirm the trailer kingpin is locked in the fifth wheel Correct answer.
  3. To verify the air lines are free of leaks
  4. To test the trailer spring brakes

Explanation

The tug test is a short pull in low gear with the trailer brakes set to confirm the kingpin is locked in the fifth wheel jaws. If the tractor moves without pulling the trailer, the coupling is not secure. It does not test lights, air lines, or spring brakes.

Question 20Vehicle Inspection and Basic Control

You are preparing to drive a vehicle with a manual transmission on a steep uphill grade. What is the safest technique to avoid rolling backward?

  1. Shift to neutral and let the vehicle roll back slightly
  2. Use the parking brake to hold the vehicle while releasing the clutch and applying power Correct answer.
  3. Hold the vehicle with the clutch on the hill
  4. Release the clutch quickly with no throttle

Explanation

Using the parking brake to hold the vehicle while you engage the clutch and apply power prevents rolling backward into a following vehicle. Slipping the clutch to hold on a hill causes wear and heat. Rolling back or releasing the clutch abruptly risks stalling or a collision.

Question 21Vehicle Inspection and Basic Control

During a pre-trip inspection, what should you check regarding the windshield and wipers?

  1. The windshield washer fluid is empty
  2. The windshield is tinted as dark as possible
  3. The wipers are removed to reduce drag
  4. The windshield is clear, free of cracks in the driver's view, and wipers work Correct answer.

Explanation

The windshield must provide a clear view, with no cracks or damage in the driver's line of sight, and the wipers must operate properly. Impaired visibility is a safety defect. Dark tint, missing wipers, and an empty washer reservoir reduce visibility and are not acceptable.

Question 22Vehicle Inspection and Basic Control

When checking the air brake system, you should watch the pressure gauge after the compressor builds to the cut-out level. What is the purpose of this check?

  1. To confirm the parking brake releases automatically
  2. To check the trailer lights are working
  3. To verify the engine idle speed
  4. To confirm the governor cuts the compressor out at the proper pressure and it holds Correct answer.

Explanation

The governor controls when the compressor stops building pressure, and the gauge should stabilize at the cut-out level without continuing to climb. A gauge that keeps rising or drops quickly indicates a governor or leak problem. This check does not test brakes releasing, lights, or idle speed.

Question 23Vehicle Inspection and Basic Control

You must drive a vehicle that has a known defect in the parking brake system. What is the correct action?

  1. Use wheel chocks instead of the parking brake
  2. Do not operate the vehicle until the parking brake is repaired Correct answer.
  3. Drive only on flat roads to reduce risk
  4. Drive at reduced speed and avoid stopping

Explanation

A defective parking brake means the vehicle cannot be safely secured and is out of service until repaired. Chocks are a temporary aid but do not replace a working parking brake. Driving on flat roads or at reduced speed does not correct the safety defect.

Question 24Vehicle Inspection and Basic Control

What is the correct sequence for a basic pre-trip inspection?

  1. Start at the driver's area, check the engine compartment, then work around the vehicle and finish with the lights Correct answer.
  2. Begin the inspection while the vehicle is moving
  3. Check only the tires and brakes since other items are optional
  4. Start with the lights and finish with the engine compartment

Explanation

A systematic pre-trip inspection starts at the driver's area, moves to the engine compartment, then proceeds around the vehicle and ends with the lights so a helper can confirm them. Following a fixed sequence prevents missed items. A moving vehicle cannot be inspected safely.

Question 25Shifting, Backing, and Turning

When you are backing a tractor-trailer and want the rear of the trailer to move toward the driver's side, in which direction should you turn the steering wheel?

  1. Toward the driver's side
  2. Away from the driver's side Correct answer.
  3. Straight ahead only, then reverse
  4. Either direction, because the trailer follows the wheel regardless

Explanation

When backing a trailer, the trailer moves opposite the direction you steer the wheel's bottom. Turning the wheel away from the driver's side swings the trailer's rear toward the driver's side, so you steer opposite the desired trailer direction.

Question 26Shifting, Backing, and Turning

Before beginning any backing maneuver in a commercial vehicle, the first thing you should do is:

  1. Turn on the four-way flashers
  2. Shift into reverse and creep slowly
  3. Get out and look at the area behind the vehicle Correct answer.
  4. Sound the horn twice

Explanation

The safe practice is to get out and check behind the vehicle before backing, because mirrors leave blind spots that can hide people, vehicles, or objects. Walking the area confirms the path is clear before you commit to the maneuver.

Question 27Shifting, Backing, and Turning

When making a right turn in a large commercial vehicle, you should:

  1. Turn sharply at the last moment to shorten the turn
  2. Turn from the left lane to increase your turning radius
  3. Keep the rear wheels close to the curb and swing the front wide Correct answer.
  4. Swing wide to the left before turning to keep the trailer clear

Explanation

A right turn in a large vehicle requires swinging the front of the vehicle wide while keeping the rear wheels close to the curb. This prevents the rear wheels from climbing the curb or striking pedestrians and objects at the corner.

Question 28Shifting, Backing, and Turning

Which statement about shifting a manual transmission in a heavy commercial vehicle is correct?

  1. Double-clutching is required on all modern transmissions
  2. Skip gears when accelerating to save time
  3. Use the clutch only to start from a stop and to shift gears Correct answer.
  4. Ride the clutch to control speed on downgrades

Explanation

In normal driving, the clutch is used to start from a standstill and to change gears, not as a speed-control device. Riding the clutch or using it to hold the vehicle on a grade causes heat and wear.

Question 29Shifting, Backing, and Turning

Why should you avoid coasting with the clutch pushed in or the transmission in neutral while driving a commercial vehicle?

  1. It reduces your ability to control speed and accelerate if needed Correct answer.
  2. It is only a problem on wet roads
  3. It causes the engine to overheat immediately
  4. It increases fuel economy beyond safe limits

Explanation

Coasting removes engine braking and leaves you unable to accelerate or slow the vehicle quickly with the drivetrain engaged. Keeping the transmission in gear preserves control, especially on grades and in traffic.

Question 30Shifting, Backing, and Turning

You are backing a 53-foot trailer into a loading dock on the right side. As the trailer begins to turn, what should you do with the steering wheel?

  1. Turn it steadily and be ready to straighten it as the trailer angles Correct answer.
  2. Turn it only after the trailer is fully in the dock
  3. Alternate rapidly between full left and full right
  4. Crank it fully and hold it until the trailer is at the dock

Explanation

Backing a long trailer requires smooth, measured steering because the trailer reacts slowly and oversteers easily. You turn steadily, then straighten the wheel as the trailer reaches the desired angle to avoid jackknifing.

Question 31Shifting, Backing, and Turning

In a manual transmission truck, what is the primary purpose of downshifting before a long downgrade?

  1. To reduce engine noise
  2. To use engine braking and avoid overheating the service brakes Correct answer.
  3. To improve fuel mileage on the descent
  4. To keep the tachometer in the green zone only

Explanation

Selecting a lower gear before a descent lets engine compression help control speed, reducing reliance on the service brakes. Overusing the brakes on a long grade can cause them to fade or fail from heat.

Question 32Shifting, Backing, and Turning

When you must back a commercial vehicle and you have a helper, where should the helper position themselves?

  1. On the driver's side mirror view, visible to you at all times Correct answer.
  2. Inside the cab next to the driver
  3. Directly behind the trailer to guide you
  4. In front of the vehicle to watch for traffic

Explanation

A spotter should stay in a position visible in your mirrors so you can see their signals throughout the maneuver. If you lose sight of the spotter, you should stop immediately until communication is restored.

Question 33Shifting, Backing, and Turning

What is the main hazard of a left turn in a large truck with a long trailer?

  1. The brakes will lock during the turn
  2. The front wheels will always strike the left curb
  3. The vehicle cannot turn left at all when loaded
  4. The trailer may swing into the adjacent lane or curb on the right Correct answer.

Explanation

In a left turn, the rear of a long trailer tracks inside the path of the front wheels and can swing wide into the adjacent lane or over a curb. You must allow extra room and check mirrors before and during the turn.

Question 34Shifting, Backing, and Turning

You are shifting a manual transmission and the transmission grinds when you select the next gear. What is the most likely cause?

  1. The engine is running too fast for the gear selected
  2. The trailer is overloaded
  3. The clutch is not fully disengaged or engine speed does not match the gear Correct answer.
  4. The tires are underinflated

Explanation

Grinding during a shift usually means the clutch is not fully disengaged or engine and transmission speeds are mismatched for the selected gear. Fully depressing the clutch and matching engine speed to the new gear reduces the clash.

Question 35Shifting, Backing, and Turning

When backing a vehicle with a trailer, at what point should you stop and re-check your position?

  1. Only after the trailer has contacted something
  2. Only when you reach the final destination
  3. Periodically, and any time you lose sight of your spotter or path Correct answer.
  4. Never, because stopping disrupts the maneuver

Explanation

Backing should be done in short, controlled segments with frequent stops to check mirrors and surroundings. Stopping whenever you lose sight of the spotter or are unsure of the path prevents collisions.

Question 36Shifting, Backing, and Turning

What does the term off-tracking describe when turning a tractor-trailer?

  1. The rear wheels following a path inside the front wheels' path Correct answer.
  2. The steering wheel returning to center on its own
  3. The trailer brakes engaging automatically in a turn
  4. The engine losing power during acceleration

Explanation

Off-tracking is the tendency of the rear wheels of a long vehicle to cut inside the path of the front wheels during a turn. The longer the wheelbase and trailer, the greater the off-tracking and the more room you must allow.

Question 37Shifting, Backing, and Turning

A driver approaching a corner in a loaded tractor-trailer should do which of the following before starting the turn?

  1. Shift into neutral to coast through the turn
  2. Speed up to carry momentum through the corner
  3. Slow down and check mirrors for the trailer's path and nearby traffic Correct answer.
  4. Hug the inside line to shorten the turn

Explanation

You should slow before entering a turn and check mirrors to account for off-tracking and traffic alongside the trailer. Carrying excess speed or hugging the inside line risks tipping, curb strikes, or collisions with adjacent vehicles.

Question 38Shifting, Backing, and Turning

On a manual transmission without a synchronized gear, what does double-clutching accomplish?

  1. It matches engine and transmission speeds to allow a smoother gear engagement Correct answer.
  2. It lets the driver shift without using the accelerator
  3. It increases the vehicle's load capacity
  4. It lets you skip the clutch on the upshift

Explanation

Double-clutching involves releasing the clutch in neutral and matching engine speed before selecting the next gear. This synchronizes the gears so they engage smoothly in a non-synchronized transmission.

Question 39Shifting, Backing, and Turning

A driver backs a trailer too far to one side and the angle between tractor and trailer becomes severe. What is the safest corrective action?

  1. Pull forward to reduce the angle, then restart the backing maneuver Correct answer.
  2. Accelerate to swing the trailer back into line
  3. Keep backing to force the trailer straight
  4. Turn the wheel fully the opposite way and continue backing

Explanation

When the angle becomes too sharp, continuing to back risks a jackknife. The safe correction is to pull forward to straighten the combination, then resume backing with smaller steering inputs.

Question 40Shifting, Backing, and Turning

Why does a longer trailer increase the risk of striking a curb during a tight right turn compared with a shorter trailer?

  1. Longer trailers have smaller tires
  2. Longer trailers shift weight to the front axle only
  3. Longer trailers have a wider turning radius at the rear, so off-tracking increases Correct answer.
  4. Longer trailers brake less effectively in turns

Explanation

The rear wheels of a longer trailer track farther inside the front wheels' path, so the amount of off-tracking grows with length. This means more room must be allowed at the curb to keep the rear wheels clear.

Question 41Space Management and Speed Control

For a CMV traveling at highway speed under ideal conditions, what does the Missouri CDL manual identify as the minimum following distance?

  1. One second for each ten feet of vehicle length
  2. One second for every ten miles per hour of speed Correct answer.
  3. Two seconds for every ten miles per hour of speed
  4. Four seconds regardless of speed

Explanation

The manual's rule of thumb is to allow at least one second of following distance for each ten feet of vehicle length at speeds below 40 mph. Above 40 mph you add one extra second, so a 60-foot vehicle at highway speed needs roughly seven seconds. This gives the driver a cushion that grows with vehicle size and speed.

Question 42Space Management and Speed Control

A CMV is traveling at 55 mph on a dry, level interstate. Roughly how much total stopping distance should the driver expect, including perception and reaction time?

  1. About 200 feet
  2. About 700 feet
  3. About 100 feet
  4. About 400 feet Correct answer.

Explanation

At 55 mph the vehicle covers about 80 feet per second, so a 1.5-second perception and reaction period alone consumes roughly 120 feet. Braking distance for a loaded combination vehicle adds several hundred feet more, putting total stopping distance near 400 feet. Drivers should plan escape routes based on this full distance, not just the braking portion.

Question 43Space Management and Speed Control

When must a Missouri CMV driver slow down below the posted speed limit?

  1. Only when a police officer directs traffic to slow
  2. Whenever conditions such as rain, fog, or heavy traffic make the posted limit unsafe Correct answer.
  3. Only when the vehicle is carrying hazardous materials
  4. Only on roads marked with a reduced advisory speed plaque

Explanation

The posted speed limit is a maximum for ideal conditions, not a target that must be maintained. A driver must reduce speed whenever weather, visibility, road surface, or traffic density makes the limit unsafe. Failing to do so can bring a citation for driving too fast for conditions even when under the posted number.

Question 44Space Management and Speed Control

A loaded tractor-trailer is descending a long, steep grade. Which technique best controls speed?

  1. Accelerate slightly to use aerodynamic drag
  2. Select a low gear before the descent and use engine braking with light brake applications Correct answer.
  3. Shift to neutral and rely on the service brakes
  4. Apply the brakes firmly and continuously all the way down

Explanation

The safe method is to choose a gear low enough that engine braking holds the vehicle near the desired speed before the grade begins. Brakes are then used in short, firm applications to trim speed rather than being dragged continuously. This prevents the brake fade and overheating that lead to runaway trucks.

Question 45Space Management and Speed Control

What is the recommended way to maintain a safe following distance behind a vehicle in a CMV?

  1. Follow closely enough that other vehicles cannot merge into the gap
  2. Estimate the gap by counting car lengths in the mirror
  3. Match the speed of the vehicle ahead exactly
  4. Watch the vehicle ahead and count seconds as it passes a fixed roadside marker Correct answer.

Explanation

The time-interval method uses a fixed object such as a sign or pavement mark; when the lead vehicle passes it, the driver counts seconds until reaching the same point. This automatically adjusts the gap for speed and is easy to apply in traffic. Counting car lengths is unreliable because it does not scale with speed.

Question 46Space Management and Speed Control

A CMV driver is being tailgated on a two-lane road. What is the safest response?

  1. Increase the space ahead of the CMV and let the tailgater pass when it is safe Correct answer.
  2. Brake sharply to warn the tailgater
  3. Speed up well above the limit to open a gap
  4. Signal the tailgater to back off using the brake lights

Explanation

When someone follows too closely, the CMV driver should lengthen the following distance to the vehicle ahead so any stop can be made gradually. This reduces the chance the tailgater rear-ends the truck and gives room to be passed. Brake-checking or speeding up escalates the hazard.

Question 47Space Management and Speed Control

Under Missouri law, what must a driver do when approached by an emergency vehicle using its siren and flashing lights?

  1. Move into the left lane and continue at the same speed
  2. Stop immediately in the travel lane
  3. Pull to the right edge of the roadway and stop until the vehicle passes Correct answer.
  4. Slow to 20 mph below the limit and keep driving

Explanation

Missouri's move-over and yield rules require drivers to pull as far as practical to the right edge of the roadway and stop until the emergency vehicle has passed. Blocking the lane or continuing at speed can delay the response and is a violation. Once the emergency vehicle passes, the driver may resume.

Question 48Space Management and Speed Control

When a CMV driver must stop on the shoulder of a highway, what should be done to warn approaching traffic?

  1. Open the hood to signal a breakdown
  2. Place a flashlight on the bumper
  3. Leave the headlights on high beam
  4. Turn on the four-way flashers and place reflective triangles behind the vehicle Correct answer.

Explanation

A stopped CMV on or near the roadway is a hazard that approaching drivers may not see in time. The manual directs drivers to activate hazard flashers and set out reflective warning triangles at the required distances. These devices give following traffic advance notice, especially at night or in poor visibility.

Question 49Space Management and Speed Control

Which factor most increases the stopping distance of a CMV on a wet roadway?

  1. The height of the driver's seat
  2. The number of axles on the trailer
  3. The color of the pavement markings
  4. Reduced tire traction and the risk of hydroplaning Correct answer.

Explanation

Water on the pavement reduces the friction between tire and road, which lengthens braking distance and can cause hydroplaning at higher speeds. Drivers should reduce speed and increase following distance when the surface is wet. Traction, not vehicle cosmetics, is the controlling factor.

Question 50Space Management and Speed Control

A CMV driver is following a motorcycle on a rural highway. How should the following distance be adjusted?

  1. Follow closely to discourage the motorcycle from changing lanes
  2. Reduce it so the motorcycle rider can see the truck
  3. Increase it to give the rider more room and time to react Correct answer.
  4. Keep the same distance used for a passenger car

Explanation

Motorcycles can stop more quickly than a loaded CMV, and a rider has far less protection in a crash. The manual advises allowing extra following distance behind motorcycles so the truck has time to react and the rider is not crowded. Tailgating a motorcycle is especially dangerous.