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Sorting Factors Into Stages
A question in our source material, worth importing because it catches so many candidates:
How is your reaction time affected by worn tyres?
The answer: not at all. Reaction time is purely human — perception, decision, movement. Tyres, brakes, and load belong entirely to the braking stage. Worn tyres lengthen your braking distance dramatically; they cannot touch your reaction time, because the car hasn't been asked to do anything yet during that stage.
The general form of the trap: questions that attach a vehicle factor to the human stage, or a human factor to the vehicle stage. Sort every factor into its stage and this entire question family falls open:
| Reaction stage (human) | Braking stage (vehicle & road) |
|---|---|
| Alcohol, drugs, medication | Tyres — tread, pressure |
| Tiredness | Brakes — condition, technique |
| Needing to decide | Road surface and friction |
| Anticipation (shrinks it) | Gradient |
| Preparedness (shrinks it) | Load |
One factor sits in both columns: speed stretches both stages — linearly in one, quadratically in the other.
Key takeaways
- Human factors → reaction; vehicle and surface factors → braking; speed → both — this sorting defuses a whole exam-question family
- Reaction time is purely human: nothing about the car can touch it
Quick check
Which of these lengthens your reaction time?