Mississippi Doubles & Triples (T) Practice Test
The endorsement for pulling two or three trailers. The test targets what changes when you add trailers: the crack-the-whip effect that amplifies every steering input at the last trailer, why the lightest trailer belongs in the rear, converter dollies and how coupling doubles differs from coupling a single, and the longer gaps and slower decisions that stability demands. It's knowledge-test-only — there's no separate skills test — but several states won't let you pull triples at all, so where you can use it depends on where you drive.
Who needs it: LTL linehaul and turnpike drivers pulling sets. Knowledge test only — no separate skills exam.
Sample practice questions
To check that air reaches the rear trailer, you:
Answer: Charge the system, open the emergency line shut-off valve at the rear of the last trailer (hear air escape), then close it — Hearing air escape at the rear emergency-line valve proves air made it all the way to the back trailer.
The first coupling step with the converter dolly is to:
Answer: Release the dolly brakes (or remove chocks) and wheel the dolly into position lined up with the rear trailer's kingpin — Position the dolly first, in line with the rear trailer's kingpin.
Why must you make sure the air lines are not crossed?
Answer: Crossed service/emergency lines mean the brakes won't respond the way you command — a safety hazard — Service (control) and emergency (supply) lines must connect to the right couplers or braking behaves wrongly.
Common mistakes on the Doubles/Triples test
- Putting the heaviest trailer in the rear — the test (and physics) wants it behind the tractor
- Forgetting the dolly coupling sequence and the extra air-line connections doubles require
- Ignoring rearward amplification — the last trailer can flip from an input the tractor barely felt
- Assuming triples are legal everywhere — several states prohibit them entirely
The Doubles & Triples (T) endorsement has no federal ELDT requirement — it's a knowledge test only, so practice is the whole game.
Official source: Mississippi Department of Public Safety, Driver Service Bureau
CDL licensing in Mississippi is administered by the Mississippi Department of Public Safety, Driver Service Bureau. Fees, scheduling, forms, and the official Mississippi CDL manual live on the official site: Mississippi DPS — official CDL page (verified 2026-08-09).
Truckcess is not affiliated with or endorsed by the Mississippi Department of Public Safety, Driver Service Bureau. Our practice tests cover the federal CDL knowledge standards (49 CFR Part 383) that every state exam is built on; exact question counts, fees, and procedures vary by state and change over time — the official site is always the authority.
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Full prep courses are one-time from $59 with 12 months of access — mytruckcess.com/cdl.
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