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Thinking Distances
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For alert drivers, reaction times are nearly always going to be the same. How far you travel whilst thinking, therefore, depends on only one thing: speed!
From our work on speed, we know that distance = speed × time. Since the reaction time is essentially constant, the thinking distance is directly proportional to speed.
This direct propotionality can be seen in the table of thinking distances shown below. For each 10 mph increase in speed, thinking distance goes up by exactly 3 m.
| Speed (mph) | Speed (m/s) | Thinking Distance (m) |
| 20 | 8·9 | 6 |
| 30 | 13·3 | 9 |
| 40 | 17·8 | 12 |
| 50 | 22·2 | 15 |
| 60 | 26·7 | 18 |
| 70 | 31·1 | 21 |
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