Driving Doubles and Triples
How the combination behaves
Every trailer's wheels track inside the path of the unit ahead - off-tracking. With two or three trailers the cut is cumulative, so the last trailer can be several feet inside your turn. Start turns from the outside of your lane, swing wide, and do not finish the turn until the last trailer clears. On tight right turns, a short swing left first (the "jug handle") keeps the rear trailer off the curb. Watch the last trailer's wheels in your mirrors as you turn; the rear of a long trailer can also swing outward and sideswipe signs, poles, or a vehicle beside you.
Stopping takes longer, and sway is a real risk. The usual causes of fishtailing are too little weight on the rear trailer's kingpin, too much speed, and sudden steering. If the rear trailer starts to sway: ease off the accelerator, hold the wheel firmly and straight, and avoid hard braking or sharp countersteering - a firm, steady application of the trailer hand valve or brakes is better than slamming them.
Do not back doubles or triples. If you have no choice, back only a short distance in a straight line. Give yourself more following distance, more room to pass, and more room at railroad crossings - you need enough space for the entire combination to clear the tracks before you start across. Crosswinds push the last trailer hardest.
Traps
Options often claim the rear trailer cuts the corner less than a single trailer (wrong - it cuts more), or that heavy braking is the cure for sway (wrong).
Rule of thumb
Turn wide, finish wide: do not complete the turn until the last trailer's wheels are past the corner.