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Difficulty: MediumSpeed and Road Conditions

You are driving a commercial motor vehicle along a rural highway covered with packed snow. As you approach a sharp curve, the posted advisory speed is 30 mph30\text{ mph}. Which of the following describes the correct procedure for managing your vehicle's speed and braking controls?

  1. A
    Reduce your speed to 20 mph20\text{ mph} before entering the curve and switch the engine retarder to its highest setting to maintain wheel control.
  2. Reduce your speed to 15 mph15\text{ mph} or less before entering the curve and ensure that the engine retarder is switched off.Answer
  3. C
    Enter the curve at the posted 30 mph30\text{ mph} advisory speed and apply steady service brakes while steering through the bend to reduce speed gradually.
  4. D
    Reduce your speed by one-third to 20 mph20\text{ mph} while navigating the curve, relying on braking distance alone to maintain a safe stopping buffer.

Answer

Reduce vehicle speed to 15 mph15\text{ mph} or less before entering the curve and ensure that the engine retarder is switched off.
According to standard commercial vehicle operation guidelines, drivers traveling on packed snow must reduce speed by half or more (slowing to 15 mph15\text{ mph} or less from a 30 mph30\text{ mph} baseline). This speed adjustment must be completed entirely before entering the curve so the vehicle can coast or lightly power through the turn without braking forces. Furthermore, engine retarders must be turned off on slippery surfaces because auxiliary braking on drive axles can easily break traction and induce a dangerous skid.

Step-by-Step Solution

1
Calculate the required speed reduction for packed snow conditions.
On packed snow, drivers must reduce speed by at least half (from 30 mph30\text{ mph} down to 15 mph15\text{ mph} or slower).
Packed snow severely decreases tire friction, requiring a substantial reduction in speed to preserve directional control.
2
Determine the proper timing for speed adjustment relative to the curve.
Decelerate to the safe target speed prior to entering the curve radius.
Braking inside a curve can lock the wheels and induce a skid because tires cannot handle simultaneous heavy braking and steering forces.
3
Set auxiliary braking devices according to road surface conditions.
Turn off the engine retarder.
Retarders apply braking force only to drive axles, which can cause the drive wheels to lose traction and trigger a jackknife on slippery surfaces.

Key Concept

Speed reduction and vehicle control adjustments on packed snow and curves
Estimated Time:1m 0s
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Topics

Speed and Road Conditions

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