Inspection of Doubles and Triples
Walking the full length of a double or triple before every trip.
Endorsement: Doubles / Triples (T) · Source: FMCSA CDL Manual (public domain)
Pre-trip inspection of a double or triple covers everything in a standard tractor-trailer pre-trip plus dozens of additional points unique to the multi-trailer configuration. Plan to spend significantly longer on a double or triple pre-trip than on a single trailer, and follow a fixed walking pattern so you do not miss anything. The standard sequence is tractor first (engine compartment, in-cab gauges, walk-around), then front trailer (front, driver-side, rear, passenger-side), then dolly, then second trailer, and so on for triples.
For each trailer, check the same items you would for a single semitrailer: kingpin and apron condition, fifth-wheel coupling visible and properly locked, slack adjusters with no excessive travel, brake chambers and air lines secure, tires (tread depth, no cuts, no mismatched dual heights), wheels (no missing or loose lugs, no oil leaks at hubs, no cracked rims), suspension components (springs, U-bolts, shock absorbers, airbags), and lights and reflectors (clean, intact, functional).
For each dolly, add the dolly fifth wheel, the pintle hook, the safety chains, the air and electrical lines, and the dolly\'s own brakes and tires. After the walk-around, return to the cab and perform the seven-step air-brake test on the entire combination, paying special attention to the leak-rate test (the federal limit is 4 psi per minute on a combination, but more trailers means more opportunities for leaks, so a triple should show only minimal leakage to be considered roadworthy). Complete the daily DVIR with all units identified by trailer number and dolly number; the federal recordkeeping rule applies to every unit in the combination.
Key terms to memorize
- converter dolly
- pintle hook
- safety chains
- crack the whip
- rear trailer
- pup trailer
Other Doubles / Triples (T) topics
- Coupling Order for Doubles and Triples — Which trailer goes where, and why the heaviest goes first.
- Converter Dollies — The two-axle dolly that turns a semitrailer into the second unit of a double.
- Handling Doubles and Triples on the Road — Following distance, lane changes, and the crack-the-whip physics.
- Prohibited Cargo and Restrictions — What you cannot legally haul in a double or triple combination.
Test what you learned
Now that you have the Inspection of Doubles and Triples material in your head, drill the Doubles / Triples (T) practice test. The questions are drawn from the same FMCSA source material this article paraphrases. For state-specific framing, jump to your state page and pick the Doubles / Triples (T) test for your jurisdiction.