Alaska Combination Vehicles CDL Practice Test

This is a free 20-question practice test for the Combination Vehicles portion of the Alaska Commercial Driver's License knowledge exam. Questions are pulled from a pool of 55 drawn from the AAMVA CDL Manual, which is the source document the Alaska Division of Motor Vehicles uses to write its actual exam.

How it works: Click an answer. The correct choice highlights in green, and you'll see a short explanation. Aim for 85% or better before you sit for the real test in Alaska.

Question 1 of 20

Combination vehicles are usually:

Easier to drive than single trucks
Harder to drive than single trucks because of length, weight, and the unique handling of articulated vehicles
The same as single trucks
Faster than single trucks

Correct. Combination vehicles (tractor-trailer rigs) are heavier, longer, and articulate at the fifth wheel — all making them more demanding than single-unit trucks.

Question 2 of 20

On a tight curve or exit ramp, a tractor-trailer is most likely to roll over because:

The trailer brakes lock
The high center of gravity creates a tipping force greater than the tires can resist
The tractor accelerates
The road is dry

Correct. Centripetal forces in a curve push the cargo outward; a high center of gravity multiplies the tipping moment. Slow before the curve.

Question 3 of 20

The most likely cause of a tractor jackknife is:

Light cargo
Drive wheels lock during braking
Slow speed
Loose load

Correct. When drive wheels lose traction (locked, oversteer, ice), the tractor pivots ahead of the trailer — a jackknife.

Question 4 of 20

When coupling, after backing under the trailer, you should:

Pull the trailer immediately
Perform a tug test (gently pulling forward in low gear with trailer brakes set) to confirm the kingpin is locked
Disconnect the air lines
Lower the landing gear

Correct. A tug test confirms the kingpin is fully engaged. Skipping it is the leading cause of trailer drops shortly after coupling.

Question 5 of 20

Cargo securement: the heaviest part of the load should be:

Loaded over the front axle area, with weight evenly distributed side to side
Loaded at the rear
Loaded on one side
Stacked on top

Correct. Loading heavy cargo to the front of the trailer over the drive axles helps with traction; loading to one side or top creates dangerous handling.

Question 6 of 20

Trailer rollover is more likely when:

Cargo is loaded low and centered
Cargo is loaded high or to one side, raising the center of gravity
Cargo is light
Trailer is empty

Correct. High cargo and uneven side-loading raise the center of gravity, increasing rollover risk on curves and ramps.

Question 7 of 20

Auxiliary equipment (refrigeration, hydraulic lift gates) on the trailer:

Has no effect on the rig
Adds weight and may change rear-axle loading; verify securement and operation
Replaces the brakes
Cannot be operated while loaded

Correct. Reefer units, lift gates, and other auxiliary equipment add weight and may shift CG. Inspect securement and check operation in pre-trip.

Question 8 of 20

Before backing under a trailer to couple, you should:

Check that the trailer height is just below the fifth wheel so the fifth wheel will lift the trailer slightly when backed under
Set the trailer at any height
Lock the trailer brakes off
Disconnect the air lines

Correct. Trailer should be just low enough that the fifth wheel will lift it slightly. Too low: the fifth wheel hits the trailer body. Too high: the fifth wheel slides under without engaging the kingpin.

Question 9 of 20

The air lines connecting the tractor and trailer are:

Red (emergency) and blue (service)
Red and yellow
Blue and yellow
Black and red

Correct. The red glad-hand carries emergency/supply air; the blue glad-hand carries service air. They cross to keep matched colors when coupling.

Question 10 of 20

Front-trailer (lead) wheels lock and the trailer behind continues forward — this is:

Trailer jackknife
Tractor jackknife
Tire blowout
Off-tracking

Correct. When the trailer wheels lose traction and the front-of-trailer pivots while the tractor continues forward, the result is a trailer jackknife.

Question 11 of 20

A combination vehicle requires more time to stop than a single vehicle because:

It is much heavier and air must travel further to reach the trailer brakes
It accelerates faster
It is shorter
Drivers wait longer

Correct. Greater weight + brake-lag in long air lines = longer stopping distance. Plan ahead.

Question 12 of 20

A jackknife happens when:

The trailer wheels skid while the tractor continues forward
The tractor pulls forward in a straight line
The trailer slides sideways while the tractor pivots
The driver brakes too lightly

Correct. Jackknife is when the drive wheels skid and the trailer continues forward, causing the tractor to pivot — the rig folds at the fifth wheel like a closing knife.

Question 13 of 20

A high-mounted trailer kingpin is dangerous because:

It will not engage the fifth wheel and the trailer can drop
It is illegal
It improves coupling
It changes color

Correct. If the trailer is too high, the fifth wheel slides under without the kingpin engaging the locking jaws. The trailer is not coupled and can drop when you pull away.

Question 14 of 20

To recover from a trailer skid, you should:

Apply more brakes
Release the brakes to let the trailer wheels regain traction
Steer hard left
Honk

Correct. Release the brakes so the trailer wheels can rotate again and re-establish traction. Continued braking will worsen the skid.

Question 15 of 20

Before uncoupling, you should:

Park on level ground, set the trailer parking brake, lower the landing gear, disconnect air and electrical lines, then release the fifth-wheel jaws
Just pull away
Disconnect electrical only
Drive forward fast

Correct. Proper sequence: park level, lower landing gear to support the trailer, disconnect lines, release jaws, then pull forward slowly. Skipping any step risks dropping the trailer.

Question 16 of 20

On a slippery surface, drive in:

Higher gears at higher RPM
A gear that minimizes torque to the drive wheels and brake earlier and gentler
The lowest gear
Whatever is fastest

Correct. Reduce engine power to drive wheels (higher gear, gentler accelerator) and brake earlier and gentler to avoid wheel spin or skid.

Question 17 of 20

Which is the proper following distance for a 60-foot rig at 50 mph?

3 seconds
6 seconds
7 seconds
12 seconds

Correct. 1 second per 10 feet at speeds below 40 mph, plus 1 extra second above 40. 60 feet = 6 seconds + 1 = 7 seconds at highway speed.

Question 18 of 20

After connecting the trailer, before pulling away, you should always:

Visually inspect the fifth-wheel/kingpin connection from outside the cab
Just trust the gauge
Honk the horn
Set the trailer brake

Correct. Always visually confirm: no gap between fifth wheel and trailer plate, jaws closed around the kingpin shank, locking lever fully in place.

Question 19 of 20

When approaching a curve in a tractor-trailer, you should:

Brake during the curve
Slow down before entering the curve
Speed up
Maintain steady speed

Correct. Slow before entering the curve. Once in the curve, accelerate gently to maintain stability. Braking in a curve invites trailer skid or rollover.

Question 20 of 20

When you supply air to the trailer for the first time after coupling, you should:

Wait until air pressure builds in the trailer reservoir, then test the trailer brakes by pulling out the trailer-supply knob
Drive away immediately
Disconnect the lines
Skip the test

Correct. Charge the trailer system. Then test the trailer brake function by tugging gently or pulling the trailer-supply knob to confirm trailer brakes apply.

About the Alaska Combination Vehicles exam

Most states administer 20 Combination Vehicles questions and require 80% to pass. The exam emphasizes the unique handling of articulated vehicles: how trailers track behind the tractor, how to prevent rollover, how to manage rearward amplification with multi-trailer combinations, and the correct sequence to couple and uncouple.

The Alaska Division of Motor Vehicles follows the federal CDL standards established by FMCSA. To earn the Combination Vehicles credential, you must answer at least 80% of the questions correctly. Many candidates score lower the first time because the test pulls from a large pool — refreshing this page will give you a different mix of questions, drawn from the same authoritative source.

Want more practice? Try the full Combination Vehicles question bank or browse all Alaska CDL practice tests.