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Difficulty: EasyDownshifting Procedures

When operating a commercial motor vehicle equipped with a manual transmission, at what point should you downshift to a lower gear when approaching a steep downgrade?

  1. A
    After entering the downgrade, while coasting in neutral to match road speed
  2. Before starting down the hill, while still on level ground or approaching the crestAnswer
  3. C
    While negotiating the steepest section or curve of the descent using heavy service brakes
  4. D
    Only after reaching the bottom of the grade, relying entirely on continuous service brake pressure during the descent

Answer

Before starting down the hill, while still on level ground or approaching the crest
Downshifting before starting down a steep hill allows the driver to harness the braking effect of the engine right from the beginning of the grade. Commercial motor vehicles must be placed in a gear that allows speed control without relying excessively on the service brakes. If a driver waits until the vehicle has started down the hill, vehicle acceleration can prevent shifting into a lower gear, resulting in a runaway vehicle scenario.

Step-by-Step Solution

1
Evaluate road conditions and identify the upcoming downgrade before reaching the crest
Determine the safe target descent speed and the appropriate lower gear required
Engine braking provides the primary speed-retarding force necessary for safe descent on steep grades
2
Slow the vehicle to the proper operating speed and downshift into the chosen gear before starting down the slope
The transmission is locked into the correct low gear before gravitational pull increases vehicle speed
Once descending, vehicle acceleration often makes it impossible to synchronize engine RPM and road speed to engage a lower gear

Key Concept

Downshifting timing prior to steep downgrades and curves
Estimated Time:45s
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Topics

Downshifting Procedures

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