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Difficulty: EasySpace for Turns

When preparing to make a left turn in a commercial motor vehicle at an intersection with two-way traffic, why must the driver reach the center of the intersection before beginning the turn?

  1. A
    To encourage trailing passenger vehicles to pass on the driver's left side
  2. To prevent the rear wheels of the vehicle from cutting across oncoming traffic lanes due to off-trackingAnswer
  3. C
    To increase vehicle speed and avoid slowing down until the turn is fully completed
  4. D
    To eliminate the need for a following distance buffer after completing the maneuver

Answer

Reaching the center of the intersection before turning prevents the vehicle's rear wheels from cutting across oncoming traffic lanes due to off-tracking.
Commercial vehicles experience significant off-tracking, meaning the rear wheels follow a shorter path than the front wheels. By driving to the center of the intersection before steering left, the driver ensures that the inward track of the rear wheels stays entirely within designated lanes rather than cutting across oncoming traffic lanes.

Step-by-Step Solution

1
Identify the turning path geometry of commercial vehicles
Rear wheels take a shorter path than front wheels during any turn, known as off-tracking or cheating.
Vehicle length and wheelbase cause the rear axle to track inward toward the center of the turning radius.
2
Apply the rule for left-turn intersection positioning
Pulling forward to the center of the intersection before initiating the steering input keeps the rear of the vehicle safely clear of oncoming lanes.
Turning too early causes the rear axle to cut across the yellow dividing line or oncoming turn bay, creating a head-on collision risk.

Key Concept

Off-tracking prevention during intersection left turns
Estimated Time:45s
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Topics

Space for Turns

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