Rear Pup Sway in Crosswind
Priya is pulling a set of 28-foot doubles on I-64 east of Louisville. The tractor has a 10-speed transmission; the lead trailer is loaded to 22,000 lb and the rear pup to 18,000 lb. A 30-mph crosswind is hitting from the right. She is running 62 mph in 10th gear, and the rear pup has begun to sway left and right, about 6 inches at first and now 18 inches. She is on a bridge with no shoulder. The converter dolly's air lines are connected, but she noticed during the pre-trip that the rear pup's brakes did not apply when she used the trailer hand valve. She has 90 miles to go. Traffic is heavy in the right lane, and the next exit is 2 miles ahead.
1. What is the correct immediate response to the rear pup sway, and why is a hard brake application dangerous?
Read the worked answer
Ease off the accelerator, hold the steering wheel straight, and avoid a hard brake application. Hard braking can transfer weight, lock wheels, and cause the trailers to jackknife or amplify the swing. If she is already braking, release the brake smoothly. She should slow gradually and look for the next safe place to stop; the bridge has no shoulder, so she should not stop on it. Once stopped, she should not continue until the rear-pup brake problem is fixed.
2. Explain rearward amplification and how it affects safe speed for doubles and triples in crosswind.
Read the worked answer
Rearward amplification is the tendency of the rear trailer to swing wider than the front trailer or tractor in a maneuver. Triples amplify more than doubles, and the effect grows with speed. In a 30-mph crosswind at 62 mph, the rear pup's 18-inch sway is a warning that speed is too high for conditions. She should reduce speed substantially, often 5 to 10 mph or more, and use smooth steering. Braking or steering sharply can make it worse. If the sway does not settle after slowing, she should stop in a safe place.
3. The rear pup brakes do not work. Can Priya continue? What checks should she make?
Read the worked answer
No. A trailer without working brakes is unsafe and out of service; she cannot legally or safely continue. She should check the glad hands, the air lines from the dolly to the pup, the shut-off valves, the relay valve, and the slack adjusters and brake chambers. If a line is kinked or a valve is closed, correcting that may restore the brakes; if not, she needs repair. She should not rely on the tractor and lead-trailer brakes to stop the set.