Driving Combination Vehicles: Turning, Tracking, and Off-Tracking
Combination driving questions test whether you can predict where the trailer will go before the tractor gets there. The exam focuses on off-tracking, swept path, mirror use, and turn setup.
Geometry you must apply
- The trailer's rear wheels do not follow the tractor's path; they cut inside the turn. This is off-tracking. A longer trailer or wheelbase increases it.
- At a 90-degree turn, the trailer tires may track several feet inside the tractor's rear tires.
- The rear of the trailer swings outward in the opposite direction of the turn - tail swing - and can strike objects beside you.
- Mirrors are the primary tool: flat mirrors show lane position, convex mirrors widen the view; check both before, during, and after the turn.
Turn setup
- Slow down before the turn, not in it.
- Approach in the proper lane; do not swing wide into another lane without checking mirrors and blind spots.
- For a right turn, move forward far enough to keep the trailer tires off the curb; turn later than a car would.
- For a left turn, do not cut the corner; keep the trailer inside the lane.
- Watch the trailer's outside rear corner for tail swing.
Worked example: A 53-foot trailer is turning right at a city corner. The driver starts the turn early, and the tractor clears the curb, but the trailer's right rear tires jump the curb. Reasoning: the trailer tracks inside the tractor path. Starting the turn early shortened the arc and pulled the trailer inward. The fix is to slow first, pull forward to square the turn, then steer later while watching the right mirror.
Traps that cost marks
- Thinking "turn wide" means swing left without checking.
- Forgetting tail swing on the outside of the turn.
- Using the mirror only at the start of the turn.
- Cutting a left turn across the inside lane.