Doubles & triples practice test
The T endorsement lets a Class A driver pull two or three trailers. The test is short and focused: converter dollies, coupling order, and why the last trailer in the set is the one that tips over.
Doubles/Triples Endorsement Question 1 of 10
To make sure air reaches all trailers in the combination, you can:
What the test covers
The questions come from Section 7 of the CDL manual:
- Rearward amplification — the crack-the-whip effect that flips the rear trailer on a sudden swerve
- Load order: heaviest trailer directly behind the tractor, lightest at the rear
- Coupling and uncoupling with a converter dolly, and the order to do it in
- Air system checks across multiple trailers — which shut-off valves are open and which are closed
- Space management: an 11-second following distance for a 100-foot triple at highway speed
- Why you never back a set of doubles
Knowledge-only, but not easy
There is no skills test for the T endorsement — just the written test, typically around 20 questions at an 80% passing bar. Most misses come from the coupling sequence and the shut-off valve logic, so drill those until the answers are mechanical.
Frequently asked
- Do I need a Class A CDL first?
- Yes. Doubles/triples is an add-on to a Class A license — the combination vehicles test knowledge is assumed, and the T endorsement extends it to multiple trailers.
- Are triples legal everywhere?
- No. Many states prohibit triples entirely and several restrict doubles length or routes. The endorsement is federal; where you can actually use it is state law.
- Is there a skills test for the T endorsement?
- No — it is a knowledge test only. States assume your Class A skills test covered vehicle handling; the T test checks you understand what changes with a second and third trailer.