Wet Bridge Jackknife on I-70
You are pulling a loaded 53-foot van on I-70 near Columbia, Missouri. The road is wet from a thunderstorm, and you are in the right lane at 50 mph with cruise control set. The trailer is lightly loaded, about 12,000 pounds, and your tractor has a newer engine brake. As you cross a bridge deck, the drive axles lose traction; the trailer begins to swing to the left, and the tractor's rear steps out to the right. You are not yet at a 90-degree angle, but the rig is rotating. Traffic is light, but a box truck is 150 feet behind, and there is no shoulder for 300 feet. You have 4 hours left on your 11-hour driving limit.
1. What type of skid is developing, and what should you do with the brakes, steering, and throttle?
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This is a drive-axle loss-of-traction event that is turning into a jackknife: the trailer is pushing the tractor, and the tractor's rear is stepping out. The rig is still rotating but not yet folded, so there is time to recover if you act smoothly.
Release the brakes, especially the drive-axle brakes, because locked or dragging drive tires cannot regain traction. Do not add power; cruise control should be cancelled immediately. Steer smoothly in the direction needed to bring the tractor back into line with the trailer, and avoid a hard counter-steer that can start a swing the other way. Keep your eyes on the path you want the front of the tractor to take, not on the trailer. Once the tires regain grip and the rig straightens, ease off the steering, keep the speed low, and look for the first safe place to stop. Do not use the engine brake during recovery.
2. Why did cruise control and the engine brake make this skid more likely, and what should you have done before the bridge?
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Cruise control is designed to maintain speed, so on a slippery bridge deck it can add throttle exactly when the drive tires need less torque. The engine brake also applies retarding force at the drive wheels; on a wet bridge, that can break traction and start a drive-axle skid. The trailer is lightly loaded, so it has less weight on its tires and less resistance to swinging. Together, these factors make a jackknife more likely.
Before the bridge, you should have cancelled cruise control in the rain, turned off or reduced the engine brake on wet pavement, and slowed below 50 mph. You should also have increased following distance and avoided any abrupt steering or braking on the bridge deck, which can be slicker than the approach. The 4 hours left on the 11-hour clock is not a reason to rush; the load and weather require a lower speed and gentler inputs.
3. After you recover, what should you do about the box truck behind and the missing shoulder?
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Do not stop in the travel lane just because the rig is straight again. The box truck is only 150 feet behind, and stopping abruptly could cause a rear-end crash. Turn on hazard flashers, keep the rig moving at a controlled low speed, and use the right lane until a shoulder or exit appears. Check the mirrors for the box truck and give yourself room to slow gradually.
Once you reach a safe shoulder or exit, stop and inspect the tires, brakes, load, and trailer connections. Look for flat-spotted tires, brake smoke, shifted cargo, or damage from the skid. If anything is wrong, do not continue until it is repaired. If the rig is sound, re-enter traffic slowly and keep cruise control off for the rest of the wet weather. Report the skid to dispatch if company policy requires it, and note the bridge location and conditions.