Combination Vehicles · Antilock Brake Systems
You are driving a tractor-trailer combination and are not sure whether the trailer has ABS. How should you brake?
Explanation
Whether ABS sits on the tractor, on the trailer, or on both units, the technique does not change: use no more brake pressure than the stop needs, and watch the rig as it slows. ABS does not require or reward a different braking technique; it only intervenes automatically if a wheel is about to lock up. This is manual-only content, topic-scoped to 49 CFR 383.111(c)(3)(ii). Using much lighter pressure invents an unnecessarily cautious technique the manual doesn't call for. Relying on the trailer hand valve repeats an established mistake, since that valve is for testing trailer brakes, not normal driving, and is unrelated to ABS status. Refusing to operate the vehicle at all overstates the situation, since driving without confirmed ABS status is not itself unsafe, only requiring normal, attentive braking.
Source: 49 CFR 383.111(c)(3)(ii)
Related Antilock Brake Systems questions
- Under 49 CFR 393.55, which combination-vehicle components must have antilock brake systems (ABS) if manufactured on or after March 1, 1998?
- A trailer was built before ABS became mandatory, and it is not clear from the outside whether it has ABS installed. According to the manual, how can a driver check?
- A combination vehicle has ABS on the trailer only. While braking hard, the driver begins to lose steering control and feels the start of a tractor jackknife. What should the driver do?