Braking and Stopping with Doubles/Triples
Braking and Stopping with Doubles/Triples
The exam tests stopping distance, brake timing, and the correct use of the trailer hand valve. A doubles/triples combination is heavier and longer, so it needs more distance and smoother inputs.
Stopping distance
- More axles and more weight mean longer stopping distance.
- Brake lag is longer: air must travel to the rear trailer.
- Increase following distance well beyond the minimum for a single trailer.
Braking technique
- Use controlled, progressive braking; avoid hard stabs that can fold the combination.
- Use engine braking on downgrades, but do not coast in neutral.
- If the rear trailer starts to swing under braking, release the brakes and steer straight to regain control.
Trailer hand valve
The trailer hand valve (spike) is for testing trailer brakes only. Do not use it while driving; it can cause a jackknife and is prohibited for normal stopping.
Worked example
You are descending a long grade with triples. Select a lower gear before the grade, use engine braking, and apply the brakes in short, firm applications. If you wait until the speed is too high, the rear trailer can push the lead trailer and cause sway.
Traps
Overusing the hand valve, riding the brakes, and leaving too little following distance. Also, assuming the rear trailer's brakes are working because the lead trailer stops.