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Difficulty: EasyMountain Driving and Steep Downgrades

When operating a commercial motor vehicle down a steep mountain downgrade, coasting with the transmission in neutral is permitted as long as the service brakes maintain the vehicle below the maximum posted speed limit.

Answer: Answer

Answer

False. Coasting in neutral down a downgrade is strictly prohibited because it eliminates engine braking and rapidly causes catastrophic brake fade.
Coasting downhill in neutral or with the clutch depressed is strictly prohibited. When the transmission is in neutral, the engine is disconnected from the drive wheels, removing all engine braking power. Forcing the friction service brakes to absorb the full force of gravity on a steep grade causes rapid overheating, lining glaze, brake fade, and potential total loss of braking ability.

Step-by-Step Solution

1
Examine commercial driving safety rules regarding transmission gear selection on mountain downgrades.
Identify that engine braking is the primary retarding force required to control speed during steep descents.
Service brakes are engineered solely to supplement engine braking and will overheat if used as the sole braking mechanism on grades.
2
Analyze the mechanical consequence of shifting into neutral on a downgrade.
Recognize that disengaging the transmission disconnects the engine from the drive wheels, eliminating all engine braking.
Without engine retarding power, the full kinetic energy of the vehicle must be absorbed by the friction brakes, creating dangerous thermal buildup.
3
Evaluate the truth value of the statement.
The statement is false because coasting in neutral is never permitted on downgrades.
Federal Motor Carrier Safety regulations and state traffic laws strictly forbid coasting in neutral down any grade.

Key Concept

Engine braking and prohibition of coasting on mountain downgrades
Estimated Time:45s
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Topics

Mountain Driving and Steep Downgrades

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