Minnesota General Knowledge CDL Practice Test

What should you do when merging?

• Merge at a much lower speed than the flow of traffic.
• Check your mirrors to be sure the gap in traffic is big enough to enter safely.
• Pull into the gap first, then check your mirrors to see if it was large enough.

Correct answer: Check your mirrors to be sure the gap in traffic is big enough to enter safely.

Your truck accelerates slowly and needs much more room than a car, so you must enter traffic through a larger gap. Your mirrors show the vehicles beside and behind you, so check them before you merge and pick a gap you can enter safely. Pull into a gap that is too small and the drivers behind you must brake hard, which can cause a crash. Signal first so other drivers know what you plan to do. Merge at the speed of the traffic; entering much slower than the flow forces everyone behind you to slow down.

Where must you keep hazardous materials shipping papers while you are driving?

• Attached to the sun visor
• In the glove box with the other papers
• In a pouch on the driver's door

Correct answer: In a pouch on the driver's door

After a crash you may be injured and unable to speak. Firefighters and police must still learn what you are hauling, so the papers have to be where they can grab them at once. The door pouch does that: it is in reach while you drive and easy to see from the open door. When you leave the cab, the papers go in the door pouch or on the driver's seat, and the emergency response information stays with them. A sun visor clip or the glove box hides the papers when seconds matter.

Which of these statements about driving through a tunnel is correct?

• There may be strong winds when exiting.
• The wind at the exit is worse for heavy trucks than light ones.
• Driving beside another vehicle is safest as you leave a tunnel.

Correct answer: There may be strong winds when exiting.

Inside a tunnel the walls block the wind. At the exit that shelter ends, so a gust can hit you all at once. Strong wind makes it difficult to stay in your lane, and the problem is worse for lighter vehicles. An empty trailer can be pushed toward the next lane. Keep a firm grip on the wheel, slow down, and do not drive alongside other vehicles as you come out.

Which of these vehicles off-tracks the most when it turns?

• Tractor with a 45-foot trailer
• 28-foot box truck
• 45-foot straight truck

Correct answer: Tractor with a 45-foot trailer

Off-tracking happens when the rear wheels take a different path from the front wheels in a turn. The longer the vehicle, the more it off-tracks. The tractor with a 45-foot trailer has the greatest overall length of the three choices. Also, the trailer's rear wheels off-track more than the rear wheels of the tractor. In a turn, this wide swing can make a large vehicle strike other vehicles or objects. Turn slowly and give the trailer room. The 45-foot straight truck pulls no trailer and is shorter overall, so it off-tracks less.

When should you sound your horn?

• To warn the drivers behind you that you are slowing down
• To tell another driver that it is safe to pass you
• If it helps to avoid a crash

Correct answer: If it helps to avoid a crash

Your horn is a warning device, not a message. Use it when the sound can prevent a crash, to alert a driver, walker, or cyclist who has not seen you. When you pass someone, tap the horn lightly if the law allows. A blast you do not need can startle people and push them into the very move you feared, so it creates danger instead of preventing it. Your brake lights, not your horn, warn the drivers behind you that you are slowing. Never use the horn to tell another driver that it is safe to pass you. Even after you sound the horn, keep driving so you can avoid a crash if the other person never hears you.

Which statement about alcohol is NOT true?

• A drinker can control how fast his or her body gets rid of alcohol.
• Alcohol passes straight into the blood, which takes it to the brain.
• BAC is determined by how much you drink, how fast you drink, and your weight.

Correct answer: A drinker can control how fast his or her body gets rid of alcohol.

Your body handles alcohol at a fixed speed. The liver processes only about one-third of an ounce of alcohol per hour, and nothing speeds it up. Only time lowers your blood alcohol; coffee and a cold shower do not. So a drinker cannot control how fast the body takes in or gets rid of alcohol, which makes that statement the false one. Drink faster than the liver can work and alcohol builds up in your blood, impairing judgment, vision, coordination and reaction time before you feel drunk. BAC does depend on how much you drink, how fast you drink, and your weight.

If ____ or more of the leaves in any leaf spring are missing, your vehicle is put out of service and cannot be driven.

• 1/4
• 1/2
• 1/3

Correct answer: 1/4

Leaf springs hold up the vehicle and its load and keep the axle in place. When leaves are missing, the spring can collapse. The frame or body can then drop onto a tire, and you can lose control or roll the vehicle over. That is why the limit is strict: if 1/4 or more of the leaves in any leaf spring are missing, the vehicle is put out of service and stays parked until it is repaired. Do not read the limit as 1/2. One-fourth is already enough, and any broken or missing leaf is dangerous.

Which statement about transporting hazardous materials is correct?

• Only materials labeled as explosives or poisons pose a risk to health and safety.
• Any truck carrying any amount of hazardous materials must have placards.
• All hazardous materials pose a risk to health, safety, and property.

Correct answer: All hazardous materials pose a risk to health, safety, and property.

Risk is built into the definition of hazardous materials: they are products that threaten health, safety, and property in transport. So the risk applies to every hazard class, not only explosives or poisons. Many hazardous products can injure or kill a person who touches them. For this reason, the shipper packages, marks, and labels them, and you refuse any leaking package instead of hauling it. Placards do not show whether a load is dangerous. The rules require placards only for certain types or quantities. A truck without placards may still carry hazardous materials.

Which of these affects a person's blood alcohol concentration (BAC)?

• Their height
• Their weight
• The time of day they drink

Correct answer: Their weight

Alcohol spreads through the blood in your body. A heavier person carries more blood, so the same drink is more diluted. A lighter person reaches a higher BAC from the same drinks. Three things set your BAC: how much you drink, how fast you drink, and your weight. Height is not one of them. The time of day does not matter. How fast you drink does, because the liver handles only about one drink per hour. The extra alcohol builds up in your blood. Driving a CMV at .04% BAC or higher is illegal, and a lower BAC still hurts your judgment, vision, and reaction time.

What is the right way to hold a steering wheel?

• With both hands, on opposite sides of the wheel
• With one hand on the top of the wheel and the other on your lap
• With both hands close together at the top of the wheel

Correct answer: With both hands, on opposite sides of the wheel

A firm grip with both hands keeps you in control when the road jolts the wheel. Hit a curb or a pothole with a loose or one-handed hold, and the wheel can pull away from you. A front tire that fails can twist the wheel out of your hands the same way. Hands on opposite sides also let you turn fast in an emergency without moving your grip first, so keep them there all the time, not just when trouble starts. One hand on top and the other on your lap leaves nothing to resist that sudden pull.

Which statement about drug use is correct?

• Taking drugs is safe if driving short distances.
• Use of drugs can lead to an accident, arrest, or both.
• Over-the-counter cold medicine is always safe to take before driving.

Correct answer: Use of drugs can lead to an accident, arrest, or both.

Drugs make you less alert and reduce your ability to drive safely. The law bans driving under the influence of any controlled substance, amphetamine, or narcotic. It also bans any other substance that makes a driver unsafe, including cold medicines that make you drowsy. Drug use leads to traffic accidents that cause death, injury, and property damage. It also leads to arrest, fines, jail sentences, and the end of your driving career. A short trip is not safer, because the drug still affects your judgment and reaction time. Never mix drugs with driving.

When may a driver without a hazardous materials endorsement drive a vehicle that carries hazardous materials?

• The driver holds a commercial learner's permit.
• The vehicle does not require placards.
• The hazardous materials are in a sealed, unbreakable container.

Correct answer: The vehicle does not require placards.

Placards are the diamond-shaped warning signs that tell other drivers and emergency crews what the load can do. The endorsement exists so the driver of a placarded load knows how to load, mark and haul it safely. The rule therefore turns on placards, not on packaging. If the material's type and quantity require placards, you need the hazardous materials endorsement. If no placards are required, you may drive the vehicle without one. A sealed container does not remove a placard requirement, and a learner's permit does not replace the endorsement. Driving a placarded load without the endorsement is a serious violation and leaves responders guessing at a crash.

What would be your total stopping distance at 55 mph on dry pavement?

• About half the length of a football field
• The length of a basketball court
• More than the length of a football field

Correct answer: More than the length of a football field

At 55 mph on dry pavement, your vehicle needs a minimum of 419 feet to stop. Three parts add up to that number: 142 feet while your brain recognizes the hazard, 61 feet while your foot reaches the brake, and 216 feet of braking. A football field is the closest picture of that much space, so hold that much room ahead of you. Leave less, and you are still braking when you reach the hazard. Half a football field or a basketball court is far too short: you cover that much road before the brakes even take hold.

You see a hazard ahead that will make you slow down. How do you warn the drivers behind you?

• Use your four-way flashers or brake lights to warn others.
• Wave the drivers behind you past when the lane looks clear.
• Turn on your high beam headlights to signal danger.

Correct answer: Use your four-way flashers or brake lights to warn others.

Your vehicle is big, so the drivers behind you cannot see the hazard you see. They do not expect you to slow down. Tap the brake pedal a few times. The flashing brake lights warn them early, while they still have room to stop. Turn on your four-way emergency flashers when you are already driving very slowly or are stopped. Without that warning, a following driver closes on you fast and hits you from behind. High beams do not help here. They shine forward, away from the drivers who need the warning, and they bother other drivers day or night.

What is the safest method to merge onto the road?

• Use your horn to alert others before merging.
• Wait for a gap in traffic large enough to enter the road safely.
• Pull out slowly and let the traffic behind you slow down.

Correct answer: Wait for a gap in traffic large enough to enter the road safely.

A loaded commercial vehicle accelerates slowly and takes up a lot of road. You need a much larger gap than a car needs. Check your mirrors and judge the gap before you move. Enter only when the gap lets you reach traffic speed without forcing anyone to brake. A heavier load needs an even bigger gap. Pull into a small gap and the traffic behind you must brake hard; a rear-end crash or a sideswipe can follow. A horn does not create space. Never assume other drivers will slow down to let you in.

Which statement about loading cargo is correct?

• Cargo does not need to be secured if it's under 100 pounds.
• Heavy cargo should be loaded on top of lighter cargo.
• State law sets the legal weight limits.

Correct answer: State law sets the legal weight limits.

States set the legal weight limits you must stay within. Each state has maximums for gross vehicle weight rating, gross combination weight rating, and axle weight. Axle limits often come from a bridge formula. It allows less weight when axles sit closer together, so heavy loads do not overload bridges and roads. Overloading hurts steering, braking, and speed control. Stopping distance grows, and brakes can fail when they work too hard. Securement is a separate rule: blocking and bracing keep cargo from sliding, whatever it weighs.

You start moving from a stop and the drive wheels begin to spin. What should you do?

• Press the brake pedal firmly.
• Increase the engine's speed.
• Take your foot off the accelerator.

Correct answer: Take your foot off the accelerator.

When drive wheels spin, the tires have lost their grip. Pressing the accelerator keeps sending power to those wheels. Take your foot off, and the power stops, so the tires can grip the road again. If you keep the power on, the spin turns into a drive-wheel skid. The back of the vehicle may slide sideways, or a trailer may jackknife. More engine speed seems like a way out, but it only makes the wheels spin faster. On wet or snowy roads with poor traction, add speed slowly and gently.

What should you do when a heavy load slows you down as you climb a hill?

• Increase your speed significantly.
• Turn on your hazard lights and stop.
• Shift to a lower gear.

Correct answer: Shift to a lower gear.

Gravity works against you on every upgrade, and a heavy load makes that pull stronger. A lower gear sends more pulling force to the drive wheels, so the truck keeps climbing instead of losing speed. The steeper the grade, the longer the grade, and the heavier the load, the lower the gear you need. Stay in too high a gear and the engine struggles, the truck slows further, and you can stall or roll back into the traffic behind you. Speeding up cannot fix this. The weight and the grade, not the throttle, are holding you back.

How should you arrange reflective triangles when parking on the roadside of a straight, level, four-lane divided highway?

• One within 10 feet of the front of the vehicle, one about 50 feet to the rear, and one about 250 feet to the rear
• One within 10 feet of the rear of the vehicle, one about 100 feet to the rear, and one about 100 feet to the front
• One within 10 feet of the rear of the vehicle, one about 100 feet to the rear, and one about 200 feet to the rear

Correct answer: One within 10 feet of the rear of the vehicle, one about 100 feet to the rear, and one about 200 feet to the rear

On a divided highway, traffic reaches you only from behind. You place all three devices toward that approaching traffic. Put one within 10 feet of the rear of the vehicle to mark where it sits. Put the second about 100 feet back and the third about 200 feet back. That spacing gives an approaching driver time to see you and change lanes. Put the devices out within ten minutes of stopping. Drivers have crashed into the rear of parked trucks because they thought the vehicle was still moving. A triangle placed in front of the vehicle warns nobody on this road.

Which statement about inspecting your wheels and rims before a trip is true?

• A wheel is safe to drive with one lug nut missing if the rest are tight.
• Rust around wheel nuts may mean that they are loose.
• A cracked rim is safe to use once the crack has been welded.

Correct answer: Rust around wheel nuts may mean that they are loose.

Wheel nuts that begin to loosen let the wheel shift slightly on the hub. That movement wears the metal and leaves rust streaks running out from the nuts. Rust there is a warning sign, so check the nuts for tightness before you drive. After any tire change, stop a short while later and check tightness again. A wheel that works loose can leave the axle at speed and cause a crash. A cracked rim is never safe, even though the wheel still turns, because the crack can let the tire come off the rim.

Your engine is overheating. Which of these is the correct practice?

• You should never remove the radiator cap on a pressurized system until the system is cooled.
• If the temperature gauge goes above the highest safe temperature, keep driving to the next truck stop.
• You must wait until the engine cools before you check the level in a see-through coolant recovery container.

Correct answer: You should never remove the radiator cap on a pressurized system until the system is cooled.

Coolant in a hot cooling system is under pressure. Opening the radiator cap too early can make steam and boiling water spray out and cause severe burns. Wait until the system has cooled before you take off the radiator cap or any other part of the pressurized system. A cap you can touch with your bare hand is probably cool enough. A see-through coolant recovery container works differently. You can check the coolant level in it while the engine is still hot. If the temperature gauge rises above the highest safe temperature, stop as soon as you safely can. Continuing to drive can cause engine failure and fire.

Which statement about backing a heavy vehicle is FALSE?

• Because you cannot see everything behind your vehicle, you should back as slowly as possible in the lowest reverse gear.
• Because you cannot see, you should back slowly until you slightly bump into the dock.
• You should check the mirrors on both sides, back toward the driver's side, and use a helper whenever you can.

Correct answer: Because you cannot see, you should back slowly until you slightly bump into the dock.

You back as slowly as possible in the lowest reverse gear. Slow speed lets you correct steering errors and stop before you hit anything. The dock is never your stopping cue. You cannot see everything behind your vehicle, so what you expect to be a slight bump can be a person, a post, or a parked load. Check the mirrors on both sides, get out and look at your path when you are unsure, and use a helper who gives you an agreed hand signal for stop. Backing slowly is correct; backing until you touch the dock is not.

You are driving a large vehicle slower than the traffic around you. Which action should you NOT take?

• Focus on maintaining a steady speed.
• Signal other drivers when it is safe to pass you.
• Stay in the right lane whenever possible.

Correct answer: Signal other drivers when it is safe to pass you.

Never signal another driver that it is safe to pass you. You cannot see what that driver sees, so you cannot judge the gap or the oncoming traffic for them. If the pass goes wrong, you could cause a crash, be blamed for it, and it could cost you many thousands of dollars. Let each driver decide when to pass. The other two choices are correct for a slow vehicle. Keep a steady speed so drivers behind you can judge their own pass. Stay in the right lane when a heavy load is slowing you down.

Which statement about emergency maneuvers is true?

• In order to turn fast, you must hold the steering wheel firmly with both hands.
• In order to maintain control, you must always use the brakes hard.
• In order to get the most clearance, you must turn as sharply as you can.

Correct answer: In order to turn fast, you must hold the steering wheel firmly with both hands.

In an emergency, stopping is not always the safest choice. If there is not enough room to stop, a turn almost always gets you around an obstacle faster than stopping would. You can turn quickly only with a firm grip on the wheel with both hands, so keep both hands there at all times. With a loose or one-handed grip, the turn is slower, and the vehicle can swerve into another lane. Do not brake hard while you turn. The wheels lock easily, and then you skid out of control instead of steering clear.

When you drive at highway speed, you should look about ___ mile ahead of your vehicle.

• 1/4
• 1/2
• 1/8

Correct answer: 1/4

Look ahead at least 12 to 15 seconds. This is the distance your vehicle will cover in that time. At highway speed, it comes to about one quarter of a mile. You need this much room because stopping or changing lanes takes a lot of distance. A view of only 1/8 mile is too short. You spot problems late and then must stop or change lanes too quickly. As you drive, keep moving your eyes between near and far.

Which brake system do you check by pumping the brake pedal three times and then holding it down for five seconds while the vehicle is parked?

• Service brakes
• Parking brakes
• Hydraulic brakes

Correct answer: Hydraulic brakes

This check is for hydraulic brakes. First, put the transmission in park. Pump the pedal three times. Then press it down and keep it there for five seconds. A good pedal stays firm and does not move. If it sinks, the system is losing pressure. Damaged hydraulic hoses, leaks or low fluid can cause a partial or total loss of brakes. The result is a longer stopping distance or a crash. The service brake test is different. In that test the vehicle rolls forward at 5 mph and stops, so you cannot do it while parked.

On a long, steep downgrade, when is the braking effect of the engine greatest?

• When the engine is near governed rpm and the transmission is in a lower gear
• When the engine is near idle rpm and the transmission is in a lower gear
• When the engine is near governed rpm and the transmission is in a higher gear

Correct answer: When the engine is near governed rpm and the transmission is in a lower gear

On a long downgrade, the engine, not the brakes, must be your main way to control speed. So you want all the engine braking you can get. Engine braking is strongest with the engine close to governed rpm and the transmission in a lower gear. That is why you shift down to a low gear before the grade begins. Low rpm or a higher gear gives less of this effect. Save your brakes so you can still slow or stop when the road or traffic calls for it.

What should you do about your tires when you drive in very hot weather?

• You should inspect your tires every two hours or every 100 miles.
• You should let air out of hot tires to bring the pressure back to normal.
• Air pressure drops as the tires heat up, so you should add air during the trip.

Correct answer: You should inspect your tires every two hours or every 100 miles.

Tires heat up as you drive, and air pressure increases with temperature. A tire that gets too hot can blow out or catch fire, so you check it before that happens. Inspect the tires every two hours or every 100 miles in very hot weather. Check the tire mounting and the air pressure each time. If a tire is too hot to touch, stay stopped until it cools. Do not let air out of a hot tire. The pressure will be too low once the tire cools.

After you start the engine, which statement about the gauges is true?

• The battery charging gauge should read zero until the engine warms up.
• The air pressure gauge will immediately show full pressure.
• The coolant temperature gauge should begin a gradual rise to normal.

Correct answer: The coolant temperature gauge should begin a gradual rise to normal.

The coolant temperature gauge shows how hot the engine is running. A cold engine warms up over several minutes, so the needle should climb slowly into the normal operating range. A needle that shoots up, or never moves at all, points to a cooling problem. An engine that overheats can stop, so catch it early. Air pressure behaves differently. It is not full at start-up. Pressure must build from 50 to 90 psi within 3 minutes. You then keep building to governor cut-out, about 120 to 140 psi.

Which action should you AVOID when helping injured people at an accident scene?

• Cool the injured person down.
• If a qualified person is helping them, stay out of the way unless asked to assist.
• Move a severely injured person only if fire or passing traffic makes it necessary.

Correct answer: Cool the injured person down.

Warmth is part of caring for the injured at an accident scene. You keep the injured person warm, and you stop heavy bleeding by applying direct pressure to the wound. Cooling the person works against that care and can leave someone who is in shock or losing blood in worse condition before trained help arrives. The other two actions are correct, not wrong. When a qualified person is already helping, you stay out of the way unless that person asks you to assist. You move a severely injured person only when fire or passing traffic makes it necessary.

Which statement about driving at night is true?

• Drivers are most alert in the hours just after midnight.
• Most roads are less crowded at night, reducing the risk of accidents.
• Many heavy vehicle accidents occur between midnight and 6 a.m.

Correct answer: Many heavy vehicle accidents occur between midnight and 6 a.m.

Your body expects to sleep after midnight, so you are less alert then. Many heavy vehicle crashes happen between midnight and 6 a.m. Fatigue plays a part in at least 15 percent of all heavy truck crashes. A tired driver reacts slowly to hazards, drifts out of the lane, and can fall asleep at the wheel. Empty roads do not make these hours safe: people who drive at night are more likely to have fall-asleep crashes. Schedule trips for the hours you are normally awake, and stop and rest when you see signs of fatigue.

How far ahead should you look while driving?

• 8-10 seconds
• 3-5 seconds
• 12-15 seconds

Correct answer: 12-15 seconds

Look at least 12 to 15 seconds ahead. This means the distance you will cover in 12 to 15 seconds. The faster you go, the farther ahead you need to look. In city traffic, that distance is roughly one block. On the highway, it is roughly a quarter of a mile. A truck needs a long distance to stop or change lanes. Looking far ahead lets you spot problems early and slow down smoothly. If you look only a few seconds ahead, you will have to stop suddenly or change lanes quickly. Three to five seconds is a following-distance gap, not how far you look.

What is a safety measure to follow when setting up reflective triangles?

• Hold the triangles between yourself and oncoming traffic.
• Stand on the traffic side of each triangle as you place it.
• Place them all in a straight line regardless of road shape.

Correct answer: Hold the triangles between yourself and oncoming traffic.

You stand at the roadside while traffic moves toward you, so keep each triangle between your body and that traffic. The bright reflective panel then faces the drivers and marks where you are while you walk out and set it down. A driver who spots you early can slow down or move over. Hold the triangle on the far side instead, and your body is the first thing an approaching car meets. Road shape matters too: if a hill or curve hides your vehicle, move the rear-most triangle farther back so drivers see it in time.

Which statement about other drivers on the road is true?

• Car drivers know how slowly a large vehicle must go to make a tight turn, so they leave room for it.
• Short-term or daily rental truck drivers are often not used to the limited vision to the sides and rear of the truck, which makes these drivers a hazard.
• When you pass a motorcyclist or a bicyclist, you can assume they have already seen you.

Correct answer: Short-term or daily rental truck drivers are often not used to the limited vision to the sides and rear of the truck, which makes these drivers a hazard.

A driver who rents a truck for a day or a week has little practice in it. The truck body blocks the view to the sides and rear, so that driver is not used to those blind areas. Treat a rental truck as a blocked-vision hazard. Expect it to change lanes or back up without seeing you, and give it room. The other options assume car drivers will leave you room and that motorcyclists and bicyclists have already seen you. Never count on that. Other drivers can miss your vehicle even when nothing blocks their view of it.

Which statement about taking medicine and driving is true?

• Prescription drugs are allowed if the doctor says they will not affect your safe driving ability.
• Medications bought over-the-counter are always safe for driving.
• Any medicine is allowed if you take it outside of working hours.

Correct answer: Prescription drugs are allowed if the doctor says they will not affect your safe driving ability.

A doctor's clearance is what makes prescription use legal. Laws prohibit using many drugs on duty and ban being under the influence of any substance that makes you unsafe. The one exception: your doctor gives you the drug and tells you it will not affect your safe driving ability. Your own opinion is not enough. Over-the-counter medicines are not automatically safe. Cold medicines can make you drowsy and affect safe driving. Time of day is not the test either. A drug still in your system makes you unsafe at the wheel. Impaired driving leads to crashes, arrest, fines, and the end of your driving career.

In which situation should you lightly tap your brakes to flash your brake lights?

• You are about to exit the road and need to slow down.
• You need to quickly change lanes.
• You're driving in heavy fog.

Correct answer: You are about to exit the road and need to slow down.

Drivers behind you cannot tell how fast they are catching a large vehicle until they are very close. A few light taps on the brake pedal flash your brake lights and warn them early. Use the same warning when a hazard ahead will make you slow down, or when you must stop in the road. Without that warning, a following driver may not slow in time and may hit your rear. Heavy fog calls for a different action: turn on your headlights and use the low beams so others can see you.

How should you respond if your vehicle begins to hydroplane?

• Release the accelerator and push in the clutch.
• Turn the steering wheel quickly.
• Brake hard to slow down.

Correct answer: Release the accelerator and push in the clutch.

When water or slush builds up on the road, your tires can ride on top of it instead of the road surface. This is hydroplaning, and it works like water skiing. Without road contact, the tires have little or no traction, so you may not be able to steer or brake. Take your foot off the accelerator and push in the clutch. The vehicle slows, and the free-turning wheels can get back onto the road. Do not brake while you hydroplane. A fast turn of the wheel does not help either, because tires without traction cannot steer. Hydroplaning can happen at speeds as low as 30 mph.

Which statement about overhead clearance is true?

• Always add an extra foot to the clearance measurement for safety.
• The weight of a cargo van changes its height.
• Overhead clearance is not affected by weather conditions.

Correct answer: The weight of a cargo van changes its height.

Hitting an overhead object is a real danger, and your true height is not fixed. An empty van rides higher than a loaded one, so a bridge you cleared when loaded may not clear when you run empty. Posted heights can also be wrong, because repaving or packed snow reduces the space under a bridge. Check the clearance for the load you carry now. If you doubt you have safe space, go slowly; if you are not sure, take another route. Adding one fixed foot is not the rule, and it can leave you short.

What blood alcohol concentration (BAC) puts you out of service for 24 hours?

• Any detectable amount under 0.04%
• A BAC of 0.04% or more
• A BAC of 0.08% or more

Correct answer: Any detectable amount under 0.04%

Alcohol slows your reaction time and weakens your judgment before you feel drunk. That is why this rule starts below the legal limit. Any detectable amount of alcohol under 0.04% puts you out of service for 24 hours. You stop driving for a full day. A BAC of 0.04% or more falls under a different rule. At that level it is illegal to drive a CMV, and you lose your CDL for at least 1 year. So 0.04% is the disqualification limit, not the 24-hour trigger. 0.08% is even further above the CMV limit.

Which statement about a skid caused by locked rear drive wheels is true?

• On a vehicle with a trailer, the trailer can push the towing vehicle sideways.
• Applying more brake pressure will stop the skid.
• Locked wheels grip the road better than rolling wheels.

Correct answer: On a vehicle with a trailer, the trailer can push the towing vehicle sideways.

With a trailer behind you, a rear-wheel skid lets the trailer push the towing vehicle sideways. This causes a sudden jackknife. Locked wheels have less traction than wheels that roll. When the rear drive wheels lock, they slide to the side and try to catch up to the front wheels. A bus or straight truck will spin out. To recover, stop braking right away. The rear wheels then roll again and regain traction, and you can counter-steer back onto your path. Pressing the brakes harder keeps the wheels locked, so the skid gets worse and the jackknife comes faster.

Which statement about accelerating a commercial vehicle is true?

• Rough acceleration can cause mechanical damage.
• If the drive wheels start to spin, press the accelerator harder.
• Speed up quickly when traction is poor, such as in rain or snow.

Correct answer: Rough acceleration can cause mechanical damage.

Speed up smoothly and gradually so the vehicle does not jerk. A jerky start puts a sudden shock load on the driveline, and that shock can break parts. When you pull a trailer, rough acceleration can damage the coupling that joins the trailer to the tractor. On a slippery road, too much power spins the drive wheels and you can lose control, so ease off the accelerator if they spin.

Backing a commercial vehicle is _____

• safe when you back toward the passenger side
• easy if you only watch your mirrors
• always dangerous

Correct answer: always dangerous

You cannot see everything behind your vehicle, so backing is always dangerous. Blind spots hide people and objects that your mirrors never show. Avoid backing whenever you can. When you must back, get out and walk your path first. Check both outside mirrors often. Back as slowly as possible in the lowest reverse gear. Backing slowly lets you correct steering errors and stop quickly if someone steps behind you. Backing toward the passenger side is not safe either: you see less on that side, so back toward the driver's side when you can. Mirrors help, but alone they still leave blind spots.

Why is it dangerous if the exhaust system is damaged?

• Fuel consumption can increase significantly.
• Poisonous fumes can enter the cab or sleeping compartment.
• Engine coolant can leak into the cab through the heater.

Correct answer: Poisonous fumes can enter the cab or sleeping compartment.

Exhaust gas contains carbon monoxide. If the exhaust system is loose, cracked or leaking, that gas can reach the cab or sleeper berth. Carbon monoxide makes you sleepy, and in large enough amounts it can kill you. A leak is even more dangerous when cab ventilation is poor, such as with the windows rolled up. So check the exhaust pipes, mufflers, tailpipes, brackets and clamps for damage, and listen for leaks. Using more fuel is a cost, not a safety risk; the danger is the gas you breathe.

What is true about notifying the authorities after an accident?

• You only need to notify the authorities about accidents that occur on highways.
• If you have a cell phone or CB radio, you should notify the authorities before you get out of your vehicle.
• You can wait until the end of the day to notify the authorities about the accident.

Correct answer: If you have a cell phone or CB radio, you should notify the authorities before you get out of your vehicle.

Calling from inside the cab starts help while the scene is still dangerous. You also stay out of passing traffic. Try to find out where you are so you can give the exact location. If you have no cell phone or CB, first protect the scene. Then phone the police or send someone to phone. Waiting until the end of the day delays help for anyone who is hurt. These steps apply to any accident, not only to one on a highway. Filing the written accident report is a separate step that comes later.

You must come to a complete stop at a railroad crossing when:

• The nature of the cargo makes a stop mandatory under the state or federal regulations.
• A green traffic signal is showing at the crossing.
• At the railway crossing, none of the warning lights are on and the barrier remains raised.

Correct answer: The nature of the cargo makes a stop mandatory under the state or federal regulations.

Some loads must stop at every grade crossing. A vehicle displaying placards stops at every crossing that is not exempt. You stop so you can look and listen before you put a heavy vehicle on the rails. A tractor-trailer needs at least 14 seconds to clear a single track, so it cannot beat a train it did not see. Dark lights and a raised gate do not prove the way is clear, because signals can fail.

How should you handle slippery road conditions?

• Make turns as gently as possible.
• Use the engine brake or speed retarder to slow down.
• Drive with your hazard lights on at all times.

Correct answer: Make turns as gently as possible.

Gentle turns are right because a slippery road gives your tires less traction. Traction is the grip between the tires and the road. With less of it, stopping takes longer and turning without a skid is harder. A sharp turn demands more grip than the tires have. Over-steering can make the wheels slide, and the truck may skid off the road or jackknife. Use only as much braking as you need. Keep the engine brake and speed retarder off on a slippery surface. Hazard lights do not add traction, so they cannot prevent a skid. Most serious skids happen when drivers go too fast for conditions.

You drive through heavy rain and your brakes get wet. What can happen when you brake?

• Engine overheating
• Stronger braking power
• Trailer jackknife

Correct answer: Trailer jackknife

Heavy rain or deep standing water can soak your brakes. Wet brakes may be weak, may apply unevenly, or may grab. If they brake unevenly, a wheel can lock and pull the tractor to one side. The trailer then swings out, and the rig can jackknife across the road. So wet brakes give you less braking power, not more. They also do not make the engine overheat. Once you are out of the water, press the brake pedal lightly for a short distance. The light pressure heats the brakes and dries them. When it is safe, make a test stop.

What can happen if there is too little weight on the driving axles?

• Poor traction
• Hard steering
• Tipping over during turns

Correct answer: Poor traction

Traction comes from weight pressing the drive tires onto the road. If the cargo is balanced so the driving axles carry too little weight, those tires lose grip. The drive wheels then spin instead of pushing the truck forward. In bad weather the truck may be unable to keep moving, and a spinning drive wheel can make you lose control. Tipping over in a turn is a different problem. A high center of gravity causes it, for example a tall stack of cargo or heavy freight loaded on top. A light drive axle does not cause it.

During a pre-trip inspection, which statement about your brakes is true?

• Small air leaks in the brake lines are normal and can be ignored.
• Brake pads are fine as long as they are not completely worn down.
• Brake shoes should not have oil, grease, or brake fluid on them.

Correct answer: Brake shoes should not have oil, grease, or brake fluid on them.

Brake shoes and pads stop your truck by rubbing against the drum or disc. Oil, grease, or brake fluid on that surface cuts the friction, so the brakes grip less and your stopping distance grows. Contaminated brake parts can also catch fire. During the walk-around, look at the shoes, pads, drums, and discs, and report any that are wet or oily. Do not wait for a pad to wear away completely. A shoe worn dangerously thin, missing, or broken is already a defect. Get it fixed before you drive.

You are driving a heavy vehicle and approaching an off-ramp that curves downhill. What is the safest way to exit the highway?

• Slow down to a safe speed before the curve.
• Wait until you are in the curve, then brake hard to slow down.
• Maintain your speed until you reach the bottom of the off-ramp.

Correct answer: Slow down to a safe speed before the curve.

A heavy truck has a high center of gravity, so it can roll over in a curve even at the posted speed. If it does not roll, the tires can lose traction and the vehicle skids straight off the road. You take the speed off while you are still straight, before you enter the curve. Braking inside the curve is the danger. There it is easier to lock the wheels and start a skid. Hard braking down the ramp can also cause brake fade. Holding your speed to the bottom leaves you braking in the worst place. Never exceed the posted speed for the curve.