Iowa Combination Vehicles CDL Practice Test

This is a free 20-question practice test for the Combination Vehicles portion of the Iowa 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 Iowa Department of Transportation Motor Vehicle Division 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 Iowa.

Question 1 of 20

When uncoupling, you should lower the landing gear:

After releasing the jaws
Before releasing the jaws so the trailer is supported when you pull away
Halfway
Not at all

Correct. Lower the landing gear and snug it against the ground before releasing the fifth-wheel jaws so the trailer doesn't drop when you pull away.

Question 2 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 3 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 4 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 5 of 20

If the trailer is too low for coupling, you should:

Crank the trailer up with the landing gear before backing under
Skip the inspection
Drive faster
Use the trailer brake

Correct. Use the landing gear hand crank to raise the trailer to the proper height (just below fifth-wheel level) before backing under.

Question 6 of 20

A sliding fifth wheel that is unlocked or improperly secured can:

Slide unexpectedly during braking or acceleration, dangerously changing handling
Improve fuel economy
Save time
Have no effect

Correct. An unsecured sliding fifth wheel can shift during braking, changing the rig's handling unpredictably. Always verify the lock pin is engaged.

Question 7 of 20

When you are backing a trailer to the right, you should turn the steering wheel:

Left to start the trailer right
Right to start the trailer right
In the same direction every time
Never use the steering wheel; just push

Correct. When backing, the trailer goes opposite to the way you initially turn the steering wheel. To make the trailer go right (passenger side), start by turning the wheel left.

Question 8 of 20

A trailer that has been sitting may have:

Brakes that need careful adjustment, rust on the kingpin, or other issues that should be inspected
No issues — trailers are static
Built-in safety
Better brakes

Correct. Trailers idle for long periods can develop brake corrosion, kingpin rust, low tires, and other issues. Inspect carefully before use.

Question 9 of 20

When you check the fifth wheel during pre-trip, you look for:

Mounting to the frame is secure, no missing or damaged parts, no visible space between the upper and lower fifth-wheel plates, locking jaws around the kingpin shank, release arm in the locked position
Only the color
Only the bolts
Only the grease

Correct. Check mount, condition, gap, jaw engagement around kingpin shank (not the head), and release-arm lock position. Lubrication should be present but not excessive.

Question 10 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 11 of 20

When making a right turn at an intersection in a tractor-trailer:

Swing to the left first to make room for the right turn
Make the turn from the right lane and swing wide as needed at the end of the turn
Make the turn at high speed
Stay in the left lane through the turn

Correct. Make the turn from the right lane. If you must swing wide, do so as you complete the turn, never before — swinging left first invites a vehicle to pass on your right.

Question 12 of 20

A sliding-tandem trailer allows you to:

Adjust the trailer-axle position to redistribute weight between trailer axles and tractor drive axles
Speed up
Cool the load
Steer the trailer

Correct. Sliding tandems shift trailer axles forward (more weight on tractor) or aft (more weight on trailer axles), helping meet axle-weight limits.

Question 13 of 20

When you "G.O.A.L." in trucking, you:

Get Off And Look — visually verify the area before backing
Go Over A Limit
Grab On And Lift
Greet Other Approaching Loaders

Correct. G.O.A.L. — Get Out And Look — is the universal driver-school rule before any tight backing maneuver.

Question 14 of 20

When you turn on a tight radius (e.g., into a tight loading dock):

Off-tracking is exaggerated; the trailer will swing far inside the line of the tractor wheels
Off-tracking disappears
Trailer follows tractor exactly
Trailer goes wide

Correct. On a tight radius, off-tracking is more pronounced. Sweep wide enough that the trailer wheels clear curbs and obstacles.

Question 15 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 16 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 17 of 20

A safe practice when arriving at a destination is to:

Pull straight in fast
Pull straight ahead, slowly, watching mirrors and clearance
Back in without help
Stop on the road

Correct. Slow approach with mirror checks gives time to identify clearance issues and pedestrians.

Question 18 of 20

When backing a tractor-trailer in a straight line, you should:

Let the trailer drift wherever it goes
Make small steering corrections to keep the trailer in line
Apply heavy brake pressure
Use the trailer hand valve

Correct. When backing straight, watch the trailer in your mirrors and make small steering corrections to keep it tracking straight. Big corrections lead to jackknifing.

Question 19 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 20 of 20

A combination-vehicle pre-trip should include:

All single-vehicle items plus fifth wheel, kingpin, sliding fifth wheel/sliding tandem locks, mud flaps, trailer brakes, lights, and trailer tires
Only the tractor
Only the trailer
Only the cargo

Correct. You inspect the entire rig — tractor + trailer + connections + cargo securement — not just the tractor.

About the Iowa 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 Iowa Department of Transportation Motor Vehicle Division 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 Iowa CDL practice tests.