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Difficulty: HardBraking Systems and ABS

An Anti-lock Braking System (ABS) helps the driver maintain steering control during severe braking. Under which road surface condition is an ABS most likely to cause an increase in the vehicle's total stopping distance compared to non-ABS braking?

  1. A
    On a newly resurfaced, dry tarmac carriageway
  2. On loose road surfaces such as gravel or unpacked snowAnswer
  3. C
    On a wet asphalt motorway with standard surface drainage
  4. D
    On a grooved concrete road surface in dry weather

Answer

On loose road surfaces such as gravel or unpacked snow
On loose surfaces such as gravel, sand, or deep snow, locked wheels naturally dig into the surface and build up a wedge of loose material in front of the tyres, helping to arrest the vehicle's forward motion. Because an Anti-lock Braking System (ABS) prevents the wheels from locking up, the tyres continue rolling over the loose upper layer without building this wedge, which can significantly lengthen the overall stopping distance even though steering control is maintained.

Step-by-Step Solution

1
Identify the primary operational mechanism of an Anti-lock Braking System (ABS).
ABS automatically pulses hydraulic brake pressure when wheel rotation sensors detect impending wheel lockup, keeping the wheels turning to preserve directional steering control.
Understanding how ABS prevents wheels from locking during emergency deceleration.
2
Analyze how vehicle tyres interact with loose surface textures when wheels lock up.
Without ABS, locked tyres scrape through loose top layers (such as gravel, sand, or deep snow) and build up a physical wedge of material directly in front of the tyres, which helps bring the car to a halt more quickly.
Evaluating surface-specific resistance and wedge-effect dynamics.
3
Determine the effect of continuous wheel rotation over loose terrain.
Because ABS prevents the tyres from locking, the wheels continuously roll over the loose surface without digging in or creating a stopping wedge, which increases the total braking distance.
Recognizing the official Highway Code and DVSA limitation of ABS on loose or uncompacted road surfaces.

Key Concept

ABS operational limitations and surface variations on loose terrain
Estimated Time:1m 0s
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Topics

Braking Systems and ABS

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