What can a quick lane change do to a truck pulling a trailer?

Turn the trailer over through the crack-the-whip effect

Uncouple the trailer from the fifth wheel

When is it especially important to avoid quick lane changes in a combination vehicle?

When the vehicle is fully loaded

In many crashes caused by the crack-the-whip effect, what overturns?

The tractor first, then the trailer

Compared with single commercial vehicles, combination vehicles usually are what?

Heavier and longer, and they need more driving skill

What happens to a truck when more cargo is piled up higher in it?

Its center of gravity rises and it turns over more easily

Its center of gravity drops and it becomes more stable

It gains traction and stops shorter

To help prevent a rollover, where should the cargo be kept?

As close to the ground as possible

The load sits to one side and the trailer leans. What is the risk?

The brakes will lock on that side

The trailer will off-track less

Where must you drive slowly to avoid rolling over a combination vehicle?

Around corners, on ramps, and off ramps

A rig has a rearward amplification of 2.0. What does that mean?

The rear trailer is twice as likely to turn over as the tractor

The rig needs twice the normal stopping distance

The tractor is twice as likely to turn over as the trailer

What can happen if you make a sudden movement with the steering wheel while pulling a trailer?

The trailer brakes could lock on

The tractor protection valve could close

How much following distance should a combination vehicle keep below 40 mph?

At least 1 second for each 10 feet of vehicle length

At least 1 second for each 20 feet of vehicle length

How fast should you drive a combination vehicle at night?

Slowly enough to see obstacles with your headlights in time to change lanes or stop gently

At the posted limit, using high beams

Faster than by day, because traffic is light

When does a large combination vehicle take longer to stop?

Stopping distance is the same either way

Why is it easy to lock up the wheels of a lightly loaded combination vehicle?

The very stiff suspension springs and strong brakes give poor traction

The trailer brakes are disconnected when empty

The tires are underinflated when empty

What is a bobtail tractor?

A tractor without a semitrailer

A tractor with a sliding fifth wheel

How does a bobtail tractor compare in stopping with a tractor-semitrailer loaded to maximum gross weight?

The bobtail takes longer to stop

The bobtail stops in half the distance

Why should you allow lots of following distance and look far ahead in any combination rig?

So you can brake early and avoid a panic stop

So you can use the trailer hand valve to slow

So other drivers can pass you on the right

Which trailers have the most trouble at railroad-highway crossings?

Trailers with low underneath clearance

A possum-belly livestock trailer is an example of what?

A low slung unit that can get stuck on a raised crossing

A trailer that never needs spring brakes

A trailer that does not off-track

Which rig setup can get stuck on a raised railroad crossing?

A single-axle tractor pulling a long trailer with landing gear set for a tandem-axle tractor

A tandem-axle tractor pulling a short trailer with the landing gear fully raised

A straight truck with no trailer

Your rig gets stuck on the railroad tracks. What do you do first?

Get out of the vehicle and away from the tracks

Stay in the cab and keep trying to move

Walk down the tracks to warn the train

Where can you find emergency notification information at a railroad crossing?

On signposts or the signal housing at the crossing

When you call 911 about a vehicle stuck on a crossing, what number is most useful to give?

The crossing's DOT number, if posted

The trailer license plate number

When is a trailer most likely to swing around after its wheels lock up?

When it is empty or lightly loaded

What is the earliest and best way to recognize that the trailer has started to skid?

Feeling the steering wheel shake

When should you check your mirrors to make sure the trailer stays where it should?

Any time you apply the brakes hard

Once a skidding trailer swings out of your lane, what is true?

It is very difficult to prevent a jackknife

The trailer will straighten out by itself

Braking harder will stop the skid

How do you get traction back when the trailer starts to skid?

Brake harder with the foot pedal

In a trailer skid, what caused the skid in the first place?

The brakes on the trailer wheels

What happens once the skidding trailer's wheels grip the road again?

The trailer starts to follow the tractor and straightens out

The trailer swings out even farther

The tractor protection valve closes

With more than one trailer, which wheels off-track the most?

The rear wheels of the last trailer

The front wheels of the tractor

Why should you keep the rear of your vehicle close to the curb in a turn?

To stop other drivers from passing you on the right

To make the trailer off-track more

You cannot finish a right turn without entering another traffic lane. What should you do?

Turn wide as you complete the turn

Swing wide to the left before starting the turn

Run the rear wheels over the curb

When backing a trailer, which way do you turn the steering wheel?

In the opposite direction from where you want to go

In the direction you want the trailer to go

You keep the wheel straight and use the brakes

While backing, the trailer starts to turn. What do you do with the steering wheel?

Turn it the other way to follow the trailer

How should you try to position your vehicle before backing a trailer?

So you can back in a straight line

So you can back toward the passenger side

Driving combination vehicles

Practice this topic56 questions

Questions and answers

What can a quick lane change do to a truck pulling a trailer?

Turn the trailer over through the crack-the-whip effect

A quick lane change whips the trailer sideways, and that crack-the-whip effect can roll it over.
Section 6 · Combination Vehicles ↗PDF, 41 MB
When is it especially important to avoid quick lane changes in a combination vehicle?

When the vehicle is fully loaded

Quick lane changes are always risky with trailers, and most of all with a full load.
Section 6 · Combination Vehicles ↗PDF, 41 MB
In many crashes caused by the crack-the-whip effect, what overturns?

Only the trailer

There are many accidents in which only the trailer turns over while the tractor stays upright.
Section 6 · Combination Vehicles ↗PDF, 41 MB
Compared with single commercial vehicles, combination vehicles usually are what?

Heavier and longer, and they need more driving skill

Their weight and length mean combination drivers need more knowledge and skill than drivers of single vehicles.
Section 6 · 6.1 – Driving Combination Vehicles Safely ↗PDF, 41 MB
What causes more than half of truck driver deaths in crashes?

Truck rollovers

Rollovers are the cause of more than half of the deaths of truck drivers in crashes.
Section 6 · 6.1.1 – Rollover Risks ↗PDF, 41 MB
What happens to a truck when more cargo is piled up higher in it?

Its center of gravity rises and it turns over more easily

Piling cargo higher raises the center of gravity, so the truck is easier to turn over.
Section 6 · 6.1.1 – Rollover Risks ↗PDF, 41 MB
How much more likely is a fully loaded rig to roll over in a crash than an empty rig?

Ten times

A fully loaded rig is ten times as likely as an empty one to roll over in a crash.
Section 6 · 6.1.1 – Rollover Risks ↗PDF, 41 MB
To help prevent a rollover, where should the cargo be kept?

As close to the ground as possible

Low cargo keeps the center of gravity low, which helps prevent rollover.
Section 6 · 6.1.1 – Rollover Risks ↗PDF, 41 MB
In which kind of vehicle is keeping the cargo low even more important?

A combination vehicle

Keeping cargo low matters in any truck, but it matters even more in combination vehicles than in straight trucks.
Section 6 · 6.1.1 – Rollover Risks ↗PDF, 41 MB
The load sits to one side and the trailer leans. What is the risk?

A rollover is more likely

A load off to one side makes the trailer lean and a rollover more likely. Keep the cargo centered and spread out.
Section 6 · 6.1.1 – Rollover Risks ↗PDF, 41 MB
What is the usual cause of rollovers?

Turning too fast

Rollovers happen when a combination vehicle is turned too fast.
Section 6 · 6.1.1 – Rollover Risks ↗PDF, 41 MB
Where must you drive slowly to avoid rolling over a combination vehicle?

Around corners, on ramps, and off ramps

Corners and ramps are where rigs roll over, so take them slowly.
Section 6 · 6.1.1 – Rollover Risks ↗PDF, 41 MB
What causes the crack-the-whip effect?

Rearward amplification

Rearward amplification is what makes the rear of a combination whip during a quick lane change.
Section 6 · 6.1.2 – Steer Gently ↗PDF, 41 MB
A rig has a rearward amplification of 2.0. What does that mean?

The rear trailer is twice as likely to turn over as the tractor

A rearward amplification of 2.0 means the rear trailer rolls over twice as easily as the tractor.
Section 6 · 6.1.2 – Steer Gently ↗PDF, 41 MB
What rearward amplification do triples have?

3.5

Triples have a rearward amplification of 3.5, the highest of the rigs shown in Figure 6.1.
Section 6 · 6.1.2 – Steer Gently ↗PDF, 41 MB
How easily can you roll the last trailer of triples compared with a five-axle tractor?

3.5 times as easily

Because of rearward amplification, the last trailer of triples rolls 3.5 times as easily as a five-axle tractor.
Section 6 · 6.1.2 – Steer Gently ↗PDF, 41 MB
How should you steer when pulling trailers?

Gently and smoothly

Steer gently and smoothly, because a sudden move of the wheel can tip the trailer over.
Section 6 · 6.1.2 – Steer Gently ↗PDF, 41 MB
What can happen if you make a sudden movement with the steering wheel while pulling a trailer?

The trailer could tip over

A sudden steering movement can be amplified at the trailer and tip it over.
Section 6 · 6.1.2 – Steer Gently ↗PDF, 41 MB
How much following distance should a combination vehicle keep below 40 mph?

At least 1 second for each 10 feet of vehicle length

Keep at least one second for every 10 feet of your vehicle length so you can avoid sudden lane changes.
Section 6 · 6.1.2 – Steer Gently ↗PDF, 41 MB
Above what speed should you add another second to your following distance?

40 mph

Add one more second to the basic following distance when going over 40 mph.
Section 6 · 6.1.2 – Steer Gently ↗PDF, 41 MB
How fast should you drive a combination vehicle at night?

Slowly enough to see obstacles with your headlights in time to change lanes or stop gently

At night, your speed must let you spot obstacles in your headlights before it is too late to react gently.
Section 6 · 6.1.2 – Steer Gently ↗PDF, 41 MB
When should you slow to a safe speed for a turn?

Before going into the turn

Get down to a safe speed before you enter the turn, not while you are in it.
Section 6 · 6.1.2 – Steer Gently ↗PDF, 41 MB
When does a large combination vehicle take longer to stop?

When it is empty

Large combinations take longer to stop empty than fully loaded, so control your speed either way.
Section 6 · 6.1.3 – Brake Early ↗PDF, 41 MB
Why is it easy to lock up the wheels of a lightly loaded combination vehicle?

The very stiff suspension springs and strong brakes give poor traction

With little weight on them, stiff springs and strong brakes give poor traction, so the wheels lock easily.
Section 6 · 6.1.3 – Brake Early ↗PDF, 41 MB
When the wheels of a lightly loaded rig lock up, what can the tractor do?

Jackknife very quickly

Locked wheels on a lightly loaded rig can let the trailer swing out and the tractor jackknife very quickly.
Section 6 · 6.1.3 – Brake Early ↗PDF, 41 MB
What is a bobtail tractor?

A tractor without a semitrailer

A bobtail is a tractor running without a semitrailer, and it needs special care when braking.
Section 6 · 6.1.3 – Brake Early ↗PDF, 41 MB
How does a bobtail tractor compare in stopping with a tractor-semitrailer loaded to maximum gross weight?

The bobtail takes longer to stop

Tests show bobtails are hard to stop smoothly and take longer to stop than a fully loaded tractor-semitrailer.
Section 6 · 6.1.3 – Brake Early ↗PDF, 41 MB
Why should you allow lots of following distance and look far ahead in any combination rig?

So you can brake early and avoid a panic stop

Space and looking ahead let you brake early instead of being surprised into a panic stop.
Section 6 · 6.1.3 – Brake Early ↗PDF, 41 MB
Which trailers have the most trouble at railroad-highway crossings?

Trailers with low underneath clearance

Low-clearance trailers can hang up on raised crossings.
Section 6 · 6.1.4 – Railroad-highway Crossings ↗PDF, 41 MB
A possum-belly livestock trailer is an example of what?

A low slung unit that can get stuck on a raised crossing

Lowboys, car carriers, moving vans and possum-belly livestock trailers are low slung and can hang up on raised crossings.
Section 6 · 6.1.4 – Railroad-highway Crossings ↗PDF, 41 MB
Which rig setup can get stuck on a raised railroad crossing?

A single-axle tractor pulling a long trailer with landing gear set for a tandem-axle tractor

Landing gear set for a tandem-axle tractor sits low on a single-axle tractor rig and can catch on a raised crossing.
Section 6 · 6.1.4 – Railroad-highway Crossings ↗PDF, 41 MB
Your rig gets stuck on the railroad tracks. What do you do first?

Get out of the vehicle and away from the tracks

Your safety comes first: leave the vehicle and get away from the tracks, then call for help.
Section 6 · 6.1.4 – Railroad-highway Crossings ↗PDF, 41 MB
Where can you find emergency notification information at a railroad crossing?

On signposts or the signal housing at the crossing

Crossing signposts or signal housings carry the emergency contact information.
Section 6 · 6.1.4 – Railroad-highway Crossings ↗PDF, 41 MB
When you call 911 about a vehicle stuck on a crossing, what number is most useful to give?

The crossing's DOT number, if posted

Describe the location with landmarks, especially the DOT number of the crossing if it is posted.
Section 6 · 6.1.4 – Railroad-highway Crossings ↗PDF, 41 MB
When is a trailer most likely to swing around after its wheels lock up?

When it is empty or lightly loaded

Locked trailer wheels make the trailer swing around, and this happens more often with a light or empty trailer.
Section 6 · 6.1.5 – Prevent Trailer Skids ↗PDF, 41 MB
What is the jackknife called when locked trailer wheels make the trailer swing around?

A trailer jackknife

When the trailer wheels lock and the trailer swings around, it is called a trailer jackknife.
Section 6 · 6.1.5 – Prevent Trailer Skids ↗PDF, 41 MB
What is the earliest and best way to recognize that the trailer has started to skid?

Seeing it in your mirrors

Watching the mirrors shows a trailer skid earliest.
Section 6 · 6.1.5 – Prevent Trailer Skids ↗PDF, 41 MB
When should you check your mirrors to make sure the trailer stays where it should?

Any time you apply the brakes hard

After any hard braking, check that the trailer is still tracking behind you.
Section 6 · 6.1.5 – Prevent Trailer Skids ↗PDF, 41 MB
Once a skidding trailer swings out of your lane, what is true?

It is very difficult to prevent a jackknife

You must catch a trailer skid early, because once the trailer leaves your lane a jackknife is hard to prevent.
Section 6 · 6.1.5 – Prevent Trailer Skids ↗PDF, 41 MB
How do you get traction back when the trailer starts to skid?

Release the brakes

Stop using the brake. Releasing the brakes lets the trailer wheels grip the road again.
Section 6 · 6.1.5 – Prevent Trailer Skids ↗PDF, 41 MB
In a trailer skid, what caused the skid in the first place?

The brakes on the trailer wheels

Trailer wheel brakes start the skid, which is why the trailer hand brake must not be used to straighten the rig.
Section 6 · 6.1.5 – Prevent Trailer Skids ↗PDF, 41 MB
What happens once the skidding trailer's wheels grip the road again?

The trailer starts to follow the tractor and straightens out

With traction back, the trailer follows the tractor and lines up again.
Section 6 · 6.1.5 – Prevent Trailer Skids ↗PDF, 41 MB
What is another name for off-tracking?

Cheating

The rear wheels following a different path from the front wheels is called off-tracking or cheating.
Section 6 · 6.1.6 – Turn Wide ↗PDF, 41 MB
Which vehicles off-track more?

Longer vehicles

The longer the vehicle, the more its rear wheels cut inside the path of the front wheels.
Section 6 · 6.1.6 – Turn Wide ↗PDF, 41 MB
With more than one trailer, which wheels off-track the most?

The rear wheels of the last trailer

Off-tracking builds along the rig, so the last trailer's rear wheels cut in the most.
Section 6 · 6.1.6 – Turn Wide ↗PDF, 41 MB
Why should you keep the rear of your vehicle close to the curb in a turn?

To stop other drivers from passing you on the right

Steer the front wide enough to clear the curb, but keep the rear close so no one can squeeze by on the right.
Section 6 · 6.1.6 – Turn Wide ↗PDF, 41 MB
You cannot finish a right turn without entering another traffic lane. What should you do?

Turn wide as you complete the turn

Turning wide as you complete the turn is better than swinging left first, which invites drivers to pass on the right.
Section 6 · 6.1.6 – Turn Wide ↗PDF, 41 MB
When backing a trailer, which way do you turn the steering wheel?

In the opposite direction from where you want to go

Backing a car or straight truck, you turn toward where you want to go. With a trailer, you turn the opposite way.
Section 6 · 6.1.7 – Backing with a Trailer. ↗PDF, 41 MB
While backing, the trailer starts to turn. What do you do with the steering wheel?

Turn it the other way to follow the trailer

After the trailer begins to turn, you turn the wheel back the other way to follow it.
Section 6 · 6.1.7 – Backing with a Trailer. ↗PDF, 41 MB
How should you try to position your vehicle before backing a trailer?

So you can back in a straight line

Whenever you can, set up to back in a straight line.
Section 6 · 6.1.7 – Backing with a Trailer. ↗PDF, 41 MB
If you must back a trailer on a curved path, which way should you back?

Toward the driver's side

Backing toward the driver's side lets you see where the trailer is going.
Section 6 · 6.1.7 – Backing with a Trailer. ↗PDF, 41 MB
Before you begin backing a trailer, how do you look at your path?

Get out and walk around the vehicle

Walk around to check side and overhead clearance in and near your path.
Section 6 · 6.1.7 – Backing with a Trailer. ↗PDF, 41 MB
Which mirrors should you use while backing a trailer?

The outside mirrors on both sides, checked often

Check both outside mirrors frequently, and get out to look again if you are unsure.
Section 6 · 6.1.7 – Backing with a Trailer. ↗PDF, 41 MB
Why should you back a trailer slowly?

So you can make corrections before you get too far off course

Backing slowly gives you time to correct before the trailer is far off its path.
Section 6 · 6.1.7 – Backing with a Trailer. ↗PDF, 41 MB
While backing, the trailer starts to drift off the proper path. How do you correct it?

Turn the top of the steering wheel in the direction of the drift

Correct drift at once by turning the top of the wheel toward the drift.
Section 6 · 6.1.7 – Backing with a Trailer. ↗PDF, 41 MB
What should you do when you need to re-position the rig while backing a trailer?

Pull forward and make pull-ups as needed

Pulling forward to set up again is a normal part of backing a trailer.
Section 6 · 6.1.7 – Backing with a Trailer. ↗PDF, 41 MB

Driving combination vehicles

Questions and answers

What can a quick lane change do to a truck pulling a trailer?

When is it especially important to avoid quick lane changes in a combination vehicle?

In many crashes caused by the crack-the-whip effect, what overturns?

Compared with single commercial vehicles, combination vehicles usually are what?

What causes more than half of truck driver deaths in crashes?

What happens to a truck when more cargo is piled up higher in it?

How much more likely is a fully loaded rig to roll over in a crash than an empty rig?

To help prevent a rollover, where should the cargo be kept?

In which kind of vehicle is keeping the cargo low even more important?

The load sits to one side and the trailer leans. What is the risk?

What is the usual cause of rollovers?

Where must you drive slowly to avoid rolling over a combination vehicle?

What causes the crack-the-whip effect?

A rig has a rearward amplification of 2.0. What does that mean?

What rearward amplification do triples have?

How easily can you roll the last trailer of triples compared with a five-axle tractor?

How should you steer when pulling trailers?

What can happen if you make a sudden movement with the steering wheel while pulling a trailer?

How much following distance should a combination vehicle keep below 40 mph?

Above what speed should you add another second to your following distance?

How fast should you drive a combination vehicle at night?

When should you slow to a safe speed for a turn?

When does a large combination vehicle take longer to stop?

Why is it easy to lock up the wheels of a lightly loaded combination vehicle?

When the wheels of a lightly loaded rig lock up, what can the tractor do?

What is a bobtail tractor?

How does a bobtail tractor compare in stopping with a tractor-semitrailer loaded to maximum gross weight?

Why should you allow lots of following distance and look far ahead in any combination rig?

Which trailers have the most trouble at railroad-highway crossings?

A possum-belly livestock trailer is an example of what?

Which rig setup can get stuck on a raised railroad crossing?

Your rig gets stuck on the railroad tracks. What do you do first?

Where can you find emergency notification information at a railroad crossing?

When you call 911 about a vehicle stuck on a crossing, what number is most useful to give?

When is a trailer most likely to swing around after its wheels lock up?

What is the jackknife called when locked trailer wheels make the trailer swing around?

What is the earliest and best way to recognize that the trailer has started to skid?

When should you check your mirrors to make sure the trailer stays where it should?

Once a skidding trailer swings out of your lane, what is true?

How do you get traction back when the trailer starts to skid?

In a trailer skid, what caused the skid in the first place?

What happens once the skidding trailer's wheels grip the road again?

What is another name for off-tracking?

Which vehicles off-track more?

With more than one trailer, which wheels off-track the most?

Why should you keep the rear of your vehicle close to the curb in a turn?

You cannot finish a right turn without entering another traffic lane. What should you do?

When backing a trailer, which way do you turn the steering wheel?

While backing, the trailer starts to turn. What do you do with the steering wheel?

How should you try to position your vehicle before backing a trailer?

If you must back a trailer on a curved path, which way should you back?

Before you begin backing a trailer, how do you look at your path?

Which mirrors should you use while backing a trailer?

Why should you back a trailer slowly?

While backing, the trailer starts to drift off the proper path. How do you correct it?

What should you do when you need to re-position the rig while backing a trailer?

Questions and answers by topic