CDL Doubles and Triples Practice Test

Updated October 27, 2026

1. In a set of triples, which trailer is most likely to turn over in a sudden lane change?
   A.The first trailerB.The middle trailerC.The last trailerD.All are equally likely
2. When coupling twin trailers, which trailer should be directly behind the tractor?
   A.The heaviest trailerB.The lightest trailerC.The newest trailerD.It doesn't matter
3. How can you check that air reaches all the trailers?
   A.Look at the gauges onlyB.Pump the brake pedal several timesC.Check the tiresD.Open the emergency line shut-off valve at the rear of the last trailer and listen for air
4. What is a converter dolly used for?
   A.Connecting the second or third trailer in a combinationB.Lifting the trailer for repairsC.Storing spare air hosesD.Converting air brakes to hydraulic brakes
5. Compared with a single trailer, doubles and triples:
   A.Are more stable and can be steered more sharplyB.Are more likely to turn over and need smoother steeringC.Need less following distanceD.Never jackknife
6. When checking air flow to all trailers in a set of doubles, the shut-off valves at the rear of the trailers should be:
   A.All closedB.All openC.Open on the front trailers and closed on the last trailerD.Closed on the front trailer and open on the last trailer
7. What connects a converter dolly to the trailer in front of it?
   A.A fifth wheel kingpinB.A glad handC.A tow strapD.A pintle hook
8. What should you check on a converter dolly during inspection?
   A.That the safety chains are secured, the air tank is drained and the lights workB.Only the color of the dollyC.That the dolly has no wheelsD.That the fifth wheel is loose
9. Why do doubles and triples need more following distance and space?
   A.They are shorter than single trailersB.They take longer to stop and are less stableC.They have better brakesD.They go faster
10. Where should the more heavily loaded trailer be placed in a set of doubles?
    A.Behind the lighter trailerB.It doesn't matterC.Directly behind the tractorD.On a separate tractor
11. Which is the best way to handle a curve in a set of triples?
    A.Brake hard in the curveB.Accelerate into the curveC.Shift gears in the middle of the curveD.Slow down before the curve, and steer smoothly
12. When coupling a second trailer, what should you check after connecting the dolly?
    A.That the coupling is secure by doing a pull test, and that there is no space between the fifth wheel platesB.That the trailer's air supply is shut offC.That the landing gear is downD.That the trailer is empty
13. In doubles and triples, a "crack-the-whip" effect means:
    A.The tractor speeds up suddenlyB.The rear trailer swings more than the front during sudden steeringC.The trailers brake one after anotherD.The air lines snap
14. Why should you drain the converter dolly's air tank?
    A.To lower the dolly's weightB.To release the trailer brakesC.To remove moisture that can freeze or damage the air brakesD.To test the safety valve
15. Before driving doubles, how can you make sure the rear trailer's brakes are working?
    A.Look at the tiresB.Disconnect the dollyC.Drive at highway speed and brake hardD.Open the emergency line shut-off at the rear of the last trailer and listen for air escaping, then close it