Doubles & Triples

Pulling two or three trailers lets one driver move more freight, but the rear trailer behaves very differently from a single trailer. It swings harder and tips over more easily, so smooth driving and careful coupling matter even more.

• Truck drivers
• LTL carriers

License requirements

• A CDL with the T (doubles/triples) endorsement, which requires a knowledge test.
• Longer combination vehicles (LCVs), including triples, also require special LCV driver training and experience under federal rules.
• Triples and some long doubles are allowed only on certain roads and in certain states, mostly in the West and on some turnpikes.

See CDL Classes & Endorsements.

The crack-the-whip effect

When you steer suddenly, each trailer swings more than the one in front of it. This is called rearward amplification. The last trailer can tip over even when the tractor and first trailer feel stable.

• Steer gently and smoothly; avoid sudden lane changes.
• Slow down well before curves and ramps.
• Leave extra following distance so you won’t need a quick swerve.
• Brake early and gently, especially on wet or icy roads.

See Rollovers & Jackknifes.

Trailer order and weight

• Put the heaviest trailer first, right behind the tractor, and the lightest at the rear.
• Keep weight low and balanced within each trailer.
• Check axle weights and length limits for the states you’ll travel. See Weight Limits & Scales.

Coupling and the converter dolly

• Dolly brakes set or wheels chocked before coupling
• Fifth wheel locked: tug test and visual check that the jaws are closed around the kingpin
• Pintle hook latched and safety chains crossed and attached
• Air and electrical lines connected, not tangled or dragging
• Rear trailer’s air shut-off valves set correctly (open on the front trailers, closed at the very back)
• Air brake test shows air reaching the last trailer
• Landing gear fully raised

See Coupling & Uncoupling and Air Brakes.

Last updated: October 2, 2026