Trailer Jackknife on a Wet Curve
On a wet two-lane highway near Hood River, you are driving a 75,000-lb combination with a 45-foot flatbed loaded with lumber. The trailer has a high center of gravity. A curve is posted 45 mph. You enter at 52 mph and, halfway through, the trailer's rear wheels lock and the trailer swings left; the tractor and trailer begin to form a V. The steering axle feels light. Your tractor has ABS, and the trailer ABS warning light was on at startup but went out after the self-test. You have 300 feet before the shoulder narrows. You must decide what action to take now, what caused the trailer jackknife, and how to prevent it on the next curve.
1. What immediate action should you take to control the trailer jackknife?
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Release the service brakes to let the locked trailer wheels roll again, and steer in the direction you want the tractor to go to straighten the combination. Do not keep braking hard; locked trailer wheels have lost lateral grip and are pushing the trailer sideways. If the tractor has ABS and you are still in a straight-line stop, hold firm pressure, but in this trailer jackknife the immediate goal is to restore trailer wheel rotation and reduce the angle. Accelerate gently only if the tractor is straight and there is room, to pull the trailer back in line. Do not overcorrect; once straight, slow gradually and pull off to inspect.
2. What caused the jackknife, and what does the ABS light tell you?
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The cause was entering a 45-mph curve at 52 mph with a high-center-of-gravity load on wet pavement, then braking hard enough to lock the trailer wheels. The locked wheels lost side grip, and the trailer's momentum swung it around the tractor. The ABS light going out after self-test means the trailer ABS is not necessarily failed, but ABS cannot overcome too much speed or a bad load. The high center of gravity and wet surface reduced both the skid and rollover margin.
3. How should you prevent this on the next curve?
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Slow to below the posted speed before the curve, and when wet, substantially below 45 mph. Brake in a straight line before entering, use a lower gear, and steer gently. Keep the load as low as possible and check that the trailer brakes are balanced. Do not brake hard while turning. If the trailer begins to swing, release the brakes and steer smoothly rather than adding more brake. Maintain space ahead and avoid a sudden change in speed mid-curve.