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Difficulty: HardCoasting and Vehicle Control

While descending a steep slope towards a junction, a driver keeps the clutch pedal fully depressed over a prolonged distance to regulate the vehicle's progress. What primary hazard does this specific action introduce regarding vehicle control and stopping performance?

  1. A
    The anti-lock braking system (ABS) will automatically disable as the drivetrain separates from the driven wheels.
  2. B
    The driver's thinking distance is substantially extended because the engine is disconnected from the transmission.
  3. The absence of engine braking places the entire workload on the footbrake, leading to brake overheating and reduced stopping effectiveness.Answer
  4. D
    The steering mechanism locks mechanically due to the lack of rotational torque transmitted from the gearbox.

Answer

The absence of engine braking places the entire workload on the footbrake, leading to brake overheating and reduced stopping effectiveness.
Holding the clutch down (coasting) separates the engine from the driven wheels, eliminating engine braking. On a downward gradient, gravity causes the car to speed up rapidly, requiring continuous footbrake application. This prolonged friction generates extreme heat, causing brake fade (loss of braking power) and compromising vehicle control when stopping at the junction.

Step-by-Step Solution

1
Identify the driver's mechanical action and definition
Holding the clutch pedal down while moving constitutes coasting under Highway Code Rule 122.
Coasting disengages the engine flywheel from the gearbox and driving wheels.
2
Analyze vehicle dynamics on a downhill slope during coasting
Engine compression resistance (engine braking) is completely eliminated, permitting gravity to accelerate the vehicle freely.
Without natural engine resistance, the vehicle requires continuous or heavy application of the service footbrake to maintain a safe speed.
3
Determine the safety consequence of prolonged footbrake use
Continuous friction generates excessive thermal energy in the brake pads and discs, causing brake fade and significantly increasing total braking distance.
Excessive heat diminishes the coefficient of friction between braking surfaces, degrading stopping performance when approaching the junction.

Key Concept

Impact of Coasting on Engine Braking and Brake Overheating (Brake Fade)
Estimated Time:1m 0s
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Topics

Coasting and Vehicle Control

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