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Difficulty: MediumSpeed on Curves and Downgrades

A commercial motor vehicle driver operating a fully loaded combination vehicle is approaching the crest of a steep, 3-mile mountain downgrade that concludes with a sharp 25 mph advisory curve at the bottom. What is the correct chronological order of procedural steps the driver must execute to safely manage speed from before starting down the grade until completing the curve?

  1. 1Select a safe target speed and shift into the proper low gear before reaching the crest and beginning the descent.
  2. 2Allow engine compression braking in low gear to hold the vehicle until speed reaches the predetermined safe speed.
  3. 3Apply the service brakes with steady pressure until vehicle speed slows to approximately 5 mph below the safe speed.
  4. 4Release the service brakes completely to allow the brake drums and linings to cool while speed gradually climbs back to the safe speed.
  5. 5Reduce speed to at or below the posted advisory speed in a straight line before entering the sharp curve at the base of the grade.

Answer

The correct chronological sequence begins with selecting the proper low gear prior to the crest, followed by allowing engine braking to reach the safe speed, executing a snub braking application to 5 mph below the safe speed, completely releasing the service brakes for cooling, and finally reducing speed below the advisory limit before steering into the curve.
Safe commercial vehicle operation dictates a strict procedural order: downshifting before the crest establishes engine braking as the primary speed controller; snub braking intermittently checks speed by 5 mph below the threshold to keep linings cool; and all curve speed reduction must occur in a straight line before entering the turn to prevent dynamic stability loss.

Step-by-Step Solution

1
Select safe target speed and downshift into low gear before beginning the downgrade.
The powertrain provides maximum engine retarding force from the very start of the descent.
Modern transmissions cannot be safely downshifted once road speed increases on a steep grade.
2
Utilize engine compression to manage vehicle acceleration up to the established safe speed.
Service brakes remain unused and cool during the initial descent phase.
Engine braking serves as the primary speed governing mechanism on downgrades.
3
Apply service brakes with firm, steady force to reduce speed by 5 mph below safe speed.
Speed drops efficiently in a short burst (about 3 seconds).
Snub braking minimizes friction contact duration, reducing cumulative thermal buildup.
4
Completely remove foot pressure from the service brake pedal.
Brake friction surfaces cool while vehicle speed slowly increases back to safe speed.
Continuous light pressure causes rapid overheating and severe brake fade, whereas complete release facilitates cooling.
5
Brake in a straight line to below the advisory speed prior to turning the steering wheel into the curve.
Tire traction is preserved entirely for lateral cornering forces.
Braking inside a curve demands simultaneous longitudinal and lateral traction, greatly increasing the risk of jackknifing or rollover.

Key Concept

Downgrade Speed Management and Pre-Curve Negotiation Sequence
Estimated Time:1m 30s
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Topics

Speed on Curves and Downgrades

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