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Difficulty: MediumCoasting and Engine Braking

You are driving down a gradual gradient towards an unexpected obstruction ahead. Why does coasting with the clutch pedal held down increase the risk of a collision?

  1. A
    It increases your thinking distance by delaying driver reaction time
  2. B
    It causes the power-assisted steering to lock completely while freewheeling
  3. It disconnects the engine from the driven wheels, eliminating engine braking and placing all braking effort on the footbrakeAnswer
  4. D
    It forces modern engine management systems to consume significantly more fuel to keep idling

Answer

Holding the clutch down disconnects the engine from the driven wheels, eliminating engine braking and forcing the footbrake to handle all slowing and stopping forces.
When the clutch is fully depressed or the gear selector is in neutral, the engine is disconnected from the drive wheels. This eliminates natural engine braking, which normally helps restrain vehicle speed on descents. Consequently, the vehicle can accelerate downhill under gravity, requiring harder application of the footbrake and increasing the risk of brake fade or inadequate stopping distance.

Step-by-Step Solution

1
Identify the mechanical consequence of depressing the clutch pedal during descent
The clutch disengages the engine from the drivetrain, eliminating engine compression resistance (engine braking).
Understanding drivetrain connectivity is essential to evaluate vehicle handling dynamics on slopes.
2
Evaluate the impact on vehicle speed control and stopping performance
Without engine braking to resist gravitational acceleration downhill, the vehicle can gain speed rapidly, placing total reliance and thermal stress on the friction brakes.
This explains why coasting compromises safety and increases stopping distances when approaching obstacles.

Key Concept

Coasting and Engine Braking
Estimated Time:50s
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Topics

Coasting and Engine Braking

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