Free Washington D.C. CDL Practice Tests — Your Complete Study Guide

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.