Drive-Wheel Skid on a Snowy Mountain Pass
You are driving a 5-axle tractor-semitrailer loaded to 74,000 lb on US-40 near Rabbit Ears Pass. Light snow is falling, and the road is packed snow over ice. You are in 8th gear with the engine brake on. Entering a right-hand curve, you touch the service brakes; the drive wheels lock, the trailer begins to swing right, and the tractor rear starts to come around. The trailer hand valve is not being used. Your speed is about 35 mph. The shoulder is soft, and a guardrail is on the outside of the curve. The tractor has ABS; you feel the pedal pulsate briefly, but as you press harder the wheels slide. The trailer ABS lamp is on. Traffic is behind you, and the next safe pullout is a quarter mile ahead.
1. What is happening in the skid, and what is the first corrective action?
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The drive wheels have locked on packed snow and ice, so the tractor rear has lost lateral grip and is trying to come around; the trailer is still pushing, which is the start of a jackknife. Pressing harder makes it worse because a locked tire cannot steer or grip. The first action is to release the service brake pressure so the drive tires can roll again, and stay off the trailer hand valve. Keep the tractor in gear and avoid a hard downshift that could lock the drives.
2. How should you steer and use the brakes to recover without causing a jackknife?
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Look and steer where you want the tractor to go, with smooth, small corrections; do not saw the wheel. As the tires roll, the tractor should straighten ahead of the trailer. If the trailer continues to swing, use a light application of power only if the drive tires have grip, and avoid abrupt braking. Do not use the trailer hand valve to pull the trailer straight; it can worsen a jackknife. If the guardrail is close, prioritize a controlled stop against the shoulder rather than a violent correction.
3. After stopping, what checks and decisions are needed before continuing on the pass?
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Once stopped, set the parking brake, turn on hazard flashers, and check the trailer angle, air lines, and fifth-wheel coupling. Look for damaged glad hands or an air leak, and confirm the trailer ABS fault did not leave the trailer brakes dragging. Chain up if conditions require it under Colorado traction or chain rules, or wait for sanding. If the combination is still straight and the brakes and coupling check out, continue at a speed that lets you stay off the brakes in curves; otherwise call for assistance. Do not continue with a trailer ABS fault and locked wheels without inspecting the brake chambers.