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?
Question 2 of 20What 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 doubles and triples: put the heaviest trailer closest to the tractor and the lightest trailer at the rear. The manual calls this the safest arrangement for handling on the road.
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.
Start Doubles/Triples Practice →