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?

Explanation

The correct response is to ease off the brake pedal, where that can be done safely, until control returns. Trailer-only ABS still helps, since it keeps the trailer tracking better under hard braking, but once the steering goes light or the tractor begins to fold, only releasing brake pressure restores traction at the steering axle. Trailer ABS cannot prevent or correct a tractor jackknife, since it only manages the trailer's own wheels. This is manual-only content, topic-scoped to 49 CFR 383.111(c)(3)(ii). Applying the trailer hand valve repeats the established mistake of using it as a correction tool, which risks worsening a skid. ABS on one unit does not compensate for a loss of control originating at another unit, so continuing to brake at the same pressure is wrong. Steering hard into the jackknife is not the taught correction and risks making an already-developing jackknife worse.

Source: 49 CFR 383.111(c)(3)(ii)