Question 1
You make a right turn pulling two trailers. Which wheels off-track the most?
The CDL combination vehicles test
To drive a tractor-trailer you need a Class A license, and for that you pass the combination vehicles knowledge test at 80%. It covers section 6 of the CDL manual: driving, trailer air brakes, coupling and inspection.
| Who takes it | Class A applicants |
|---|---|
| Pass mark | Each test: at least 80% right (49 CFR 383.135) |
| Below 80% | No Class A permit or license |
| Manual section | 6: driving, air brakes, ABS, coupling, inspecting |
What it covers
- 6.1 Driving combination vehicles safely: rollover, crack-the-whip, braking early, railroad crossings and off-tracking on turns.
- 6.2 Combination vehicle air brakes: the trailer hand valve, tractor protection valve, trailer air supply control and the service and emergency lines.
- 6.3 Antilock brakes on tractors and trailers.
- 6.4 Coupling and uncoupling a tractor-semitrailer, step by step.
- 6.5 Inspecting a combination vehicle, including the coupling system and the trailer brake tests.
Where people slip
Most mistakes are about the air lines and valves: which line supplies the trailer brakes, what the tractor protection valve does when the trailer breaks away, and when the trailer air supply knob pops out. The other common one is rearward amplification: a quick steering move makes the last trailer swing hardest.
Try 3 questions
Question 2
If the trailer breaks away from the tractor, what is the tractor protection valve there to do?
Question 3
After coupling, how far should you raise the landing gear before you drive away?
Next step
Questions people ask
Do I need the combination test for a Class A CDL?
Yes. Federal rule says an applicant who scores below 80% on the combination vehicles test may not be issued a Class A permit or license.
What is on the CDL combination test?
Section 6 of the CDL manual: driving combinations safely, trailer air brakes and ABS, coupling and uncoupling, and inspecting a combination vehicle.
Is the combination test hard?
It is short and focused. Learn the air lines and valves and the coupling steps, and practice until you are above 80% every time.