Pre-Trip Inspection & Safety Systems
10 free questions, part of the Doubles/Triples (T) Endorsement CDL practice test
ELDT.io's pre-trip inspection bank has 10 free practice questions on the walk-around checks specific to doubles and triples, on top of the standard pre-trip. Expect questions on locking the lower fifth wheel jaws around the kingpin, setting rear shut-off valves correctly, checking air flow all the way to the last trailer, and testing converter dolly brakes and ABS. Most of these items come straight from 49 CFR 383.115(e), the catch-all section for operating practices not covered elsewhere.
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What's different about the pre-trip inspection for doubles and triples?
You add checks the standard single-trailer pre-trip doesn't cover: the lower fifth wheel on each converter dolly, the rear shut-off valves on every trailer, air flow reaching the last trailer in the string, and the converter dolly's own brakes and ABS.
How do you check that air is flowing to all trailers before driving?
Open the rear shut-off valves at the back of the last trailer and listen for air escaping from both the service and emergency lines. If you don't hear air from both lines, check every connection and shut-off valve back up the string for one that's closed or disconnected.
What safety feature is required on converter dollies built after March 1998?
Converter dollies manufactured on or after March 1, 1998 must have an antilock braking system (ABS), per 49 CFR 393.55. You can confirm it's present by looking for the ABS malfunction indicator lamp on the dolly.
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