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Difficulty: MediumStopping and Following Distances

According to the UK Highway Code, a vehicle's overall stopping distance consists of thinking distance (the distance travelled while the driver reacts) and braking distance (the distance travelled while the brakes are applied). On a dry, level road in good conditions, which official metric measurement matches each individual stopping distance component at 40 mph40\text{ mph} and 60 mph60\text{ mph}?

  • Thinking distance when travelling at 40 mph40\text{ mph}12 metres12\text{ metres}
  • Braking distance when travelling at 40 mph40\text{ mph}24 metres24\text{ metres}
  • Thinking distance when travelling at 60 mph60\text{ mph}18 metres18\text{ metres}
  • Braking distance when travelling at 60 mph60\text{ mph}55 metres55\text{ metres}

Answer

Thinking distance at 40 mph40\text{ mph} matches 12 metres12\text{ metres}; Braking distance at 40 mph40\text{ mph} matches 24 metres24\text{ metres}; Thinking distance at 60 mph60\text{ mph} matches 18 metres18\text{ metres}; Braking distance at 60 mph60\text{ mph} matches 55 metres55\text{ metres}.
According to the UK Highway Code, total stopping distance is calculated by adding thinking distance and braking distance. For 40 mph40\text{ mph}, the breakdown is 12 metres12\text{ metres} thinking distance and 24 metres24\text{ metres} braking distance (total 36 metres36\text{ metres}). For 60 mph60\text{ mph}, the breakdown is 18 metres18\text{ metres} thinking distance and 55 metres55\text{ metres} braking distance (total 73 metres73\text{ metres}).

Step-by-Step Solution

1
Determine the thinking distance components for each speed
Thinking distance is 12 metres12\text{ metres} at 40 mph40\text{ mph} and 18 metres18\text{ metres} at 60 mph60\text{ mph}
Thinking distance increases linearly with vehicle speed because reaction time remains relatively constant.
2
Determine the braking distance components for each speed
Braking distance is 24 metres24\text{ metres} at 40 mph40\text{ mph} and 55 metres55\text{ metres} at 60 mph60\text{ mph}
Braking distance increases quadratically with speed as kinetic energy quadruples when speed doubles.
3
Pair each speed component with its respective metric distance
All four components are correctly matched to their Highway Code values
Overall stopping distance equals thinking distance plus braking distance (36 metres36\text{ metres} at 40 mph40\text{ mph} and 73 metres73\text{ metres} at 60 mph60\text{ mph}).

Key Concept

Highway Code stopping distance component breakdown (thinking distance vs braking distance)
Estimated Time:1m 0s
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Topics

Stopping and Following Distances

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