The mock samples coupling, air connections, trailer control, inspections, backing, turning, rollover prevention, and emergency response.
01Fifth wheel
02Air system
03Handling
04Braking
05Uncoupling
06Pre-trip checks
PRACTICE MODE
Combination Vehicles Mock Test
Questions appear in a new order on each attempt. Choose one answer, review the explanation, and use Back or Next to move through the test.
Question 1 of 25Score 0
What should be checked before connecting to a trailer?
Answer: The trailer is secured against movement A trailer can move when contacted unless its brakes are set or wheels are chocked as required. Secure it before coupling. Study: Combination Vehicles — coupling
Where must the fifth-wheel locking jaws close?
Answer: Around the kingpin shank The jaws must lock around the narrow shank, not rest on the kingpin head. A visual inspection is required after coupling. Study: Combination Vehicles — fifth wheel
What should the driver see between the fifth wheel and trailer apron after coupling?
Answer: No visible gap The trailer apron should lie flat on the fifth wheel with no gap. A gap can indicate a high hitch or incomplete coupling. Study: Combination Vehicles — coupling inspection
How should coupling security be tested before fully raising the landing gear?
Answer: Apply trailer brakes and gently pull forward A gentle tug against the set trailer brakes checks whether the fifth wheel holds the kingpin. It supplements, not replaces, a visual inspection. Study: Combination Vehicles — coupling check
What should be verified about the fifth-wheel release arm after coupling?
Answer: It is seated in the locked position The release arm should indicate a locked mechanism and the safety latch should be engaged where equipped. Any doubt requires recoupling and reinspection. Study: Combination Vehicles — fifth wheel
How should air and electrical lines be routed between tractor and trailer?
Answer: With enough slack for turns but not enough to drag Lines need room for normal articulation without pinching, snagging, or dragging. Secure them and check connections before moving. Study: Combination Vehicles — connections
What color usually identifies the emergency or supply air line?
Answer: Red Red commonly identifies the emergency or supply line, while blue identifies the service line. Do not rely on color alone if connectors or markings are unclear. Study: Combination Vehicles — air lines
What color usually identifies the trailer service air line?
Answer: Blue Blue commonly identifies the service line carrying brake-application pressure. Correct gladhand connection is vital to trailer braking. Study: Combination Vehicles — air lines
What should be done after connecting the trailer air lines?
Answer: Check that gladhands are sealed and lines are secure A poor seal leaks air and can impair trailer braking. Inspect the seals, listen for leaks, and keep lines from rubbing or dragging. Study: Combination Vehicles — connections
When should the landing gear be raised fully?
Answer: After a secure coupling has been confirmed Confirm the jaws, release arm, apron contact, and tug test first. Then raise the landing gear completely and secure the crank handle. Study: Combination Vehicles — coupling sequence
Why should the landing-gear crank handle be secured?
Answer: To keep it from extending or causing damage A loose handle can swing, catch, or damage equipment. Stow it in its keeper after the gear is fully raised. Study: Combination Vehicles — landing gear
Before uncoupling, how should the tractor and trailer be positioned?
Answer: In a straight line on firm, level ground when possible Straight, stable positioning reduces strain on the coupling and helps prevent trailer movement or landing-gear damage. Secure the vehicle before beginning. Study: Combination Vehicles — uncoupling
What must support the trailer before the tractor is pulled away?
Answer: The landing gear on firm ground Lower the landing gear until it firmly supports the trailer, using supports if the ground is soft. A loaded trailer can sink or tip on weak ground. Study: Combination Vehicles — uncoupling
Why should the trailer wheels be chocked during uncoupling when needed?
Answer: To prevent the trailer from moving The trailer can roll when the tractor pulls away or air pressure changes. Brakes and wheel chocks provide secure restraint as conditions require. Study: Combination Vehicles — uncoupling
When disconnecting air lines, where should gladhands be placed?
Answer: On dummy couplers or secure holders Dummy couplers keep dirt and water out of the lines. Secure storage also prevents damage while the tractor is away. Study: Combination Vehicles — uncoupling
After unlocking the fifth wheel during uncoupling, how far should the tractor initially pull?
Answer: Just far enough to clear the kingpin while the frame remains under the trailer Keeping the tractor frame under the trailer briefly provides support if the landing gear fails. Stop and verify stability before pulling completely clear. Study: Combination Vehicles — uncoupling
Why should a driver avoid backing a combination vehicle when possible?
Answer: It creates large blind spots and jackknife risk Long combinations are difficult to control in reverse and small errors grow quickly. Plan routes and parking to minimize backing. Study: Combination Vehicles — backing
When backing a trailer, what steering correction is best?
Answer: Small, slow corrections Trailers respond with a delay, and large inputs can quickly create a jackknife. Use both mirrors, pull up as needed, and get out to look. Study: Combination Vehicles — backing
If the trailer drifts too far while backing, what should the driver do?
Answer: Pull forward to reset the angle A pull-up is a safe correction, not a failure. Resetting the combination avoids a worsening angle or blind-side collision. Study: Combination Vehicles — backing
Why is driver-side backing preferred when a choice exists?
Answer: Visibility is generally better on the driver side Sight-side backing gives a better view of the trailer path. It still requires slow movement, mirror checks, and getting out to look. Study: Combination Vehicles — backing
During a combination pre-trip inspection, what should be checked at the fifth wheel?
Answer: Mounting, lubrication, jaws, kingpin, and release mechanism The coupling must be securely mounted, properly locked, and free of damage. A complete inspection checks both the mechanism and its connection to the frame. Study: Combination Vehicles — inspection
What should be checked where the fifth wheel mounts to the tractor frame?
Answer: No missing or damaged mounting parts and no illegal welds Loose or damaged mounts can allow the coupling to fail. Inspect brackets, bolts, and welds as required by the vehicle design. Study: Combination Vehicles — inspection
What should be checked on the trailer landing gear?
Answer: It is fully raised, undamaged, and the handle is secured Landing gear left partly down can strike the road. Inspect both legs, braces, pads, and the crank mechanism. Study: Combination Vehicles — inspection
What should the driver check about trailer air lines during inspection?
Answer: They are connected, sealed, supported, and free of damage Leaks, abrasion, kinks, or poor routing can cause brake failure. Lines must flex through turns without snagging. Study: Combination Vehicles — inspection
How is trailer brake operation commonly checked at low speed?
Answer: Use the trailer hand valve and feel for braking A low-speed hand-valve check confirms the trailer brakes respond. The hand valve is for testing, not normal stopping. Study: Combination Vehicles — brake test
Answer from memory so your first score shows which topics need work.
02
Review the explanations
Return to the cited handbook section whenever an idea is unclear.
03
Retake after review
Aim for consistent mastery, not memorizing the position of an answer.
FACT-CHECKED STUDY BASIS
Official handbook sources
Questions are original study material based on standard CDL manual topics. Requirements can vary by state and hazardous-material rules can change, so confirm details in your current state manual and applicable federal guidance.
Important: This independent study site is not affiliated with FMCSA, TSA, PHMSA, or any state DMV. It does not replace official guidance or professional instruction.