Unlock LTL Jobs
Required for FedEx Freight, XPO, Old Dominion, and all LTL carriers.
The T endorsement lets you pull two or three trailers. LTL carriers pay a premium for this skill — and it's only 20 extra test questions.
- ✓ Required for LTL freight companies
- ✓ Class A CDL prerequisite
- ✓ Only 20 questions on the test
Try The 2026 Doubles & Triples Test
When pulling triples, which trailer should be the heaviest?
What is the major cause of the "Crack-the-Whip" effect?
T Endorsement Study Guide
The Doubles/Triples test focuses on coupling multiple trailers, weight distribution, and the unique handling challenges of longer combinations.
1. The Crack-the-Whip Effect
When the lead trailer swerves, that motion is amplified at the rear trailer. The last trailer in a set of triples can experience forces 3x greater than the first. This is the #1 cause of rollovers.
Prevention: Steer smoothly, maintain low speed in curves, and never make sudden lane changes. If you feel a sway developing, do NOT brake — let off the accelerator gently.
2. Coupling Converter Dollies
The converter dolly connects the second (and third) trailers. Key steps:
- Secure the dolly under the rear trailer's pintle hook
- Lock the pintle hook latch
- Connect both air lines (service and emergency)
- Raise the dolly landing gear
- Perform a visual inspection of all connections
3. Weight Distribution
For triples: place the heaviest trailer closest to the tractor, the lightest in the middle, and the next heaviest at the rear. This minimizes the crack-the-whip effect.
Frequently Asked Questions
How many questions are on the Doubles/Triples test? ▾
What is the Crack-the-Whip effect? ▾
Do I need a Class A CDL for Doubles/Triples? ▾
Doubles & Triples
Ready for Your T Endorsement?
Master coupling dollies, crack-the-whip prevention, and weight distribution.