Theory Mastery

Braking-distance formula: square divided by two

The textbook formula for braking distance on a dry road is (speed ÷ 10)² ÷ 2 — at 50 km/h: 5² ÷ 2 = 12.5 m. Leaving out the division by two ((speed ÷ 10)² = 25 m) is not the textbook formula but a doubled braking distance.

Source: Speed, distance & stopping distance · checked 2026-10-23

How the exam asks it

About The braking-distance rule of thumb: (speed:10)² : 2: which statement is WRONG?

  1. If speed doubles, braking distance also doubles (a linear relationship).
  2. The rule of thumb literally is '(speed(km/h):10) x (speed(km/h):10) : 2', with the book's own worked examples 50 km/h = 12.50 m, 80 km/h = 32.00 m, 130 km/h = 84.50 m.
  3. Stopping distance = reaction distance + braking distance.
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Correct answer: If speed doubles, braking distance also doubles (a linear relationship).

'braking distance increases progressively: if you drive 2x as fast, your braking distance becomes 4x as long.' At 40 km/h braking distance is 8.00 m; at 80 km/h (2x as fast) it is 32.00 m — 4x, not double

Why learners get this wrong: Braking distance = (speed:10) squared, with no further division (so 25 m at 50 km/h, 100 m at 100 km/h).

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On the A35 near Nijverdal you are driving 100 km/h in the right-hand lane. What is your braking distance per the book formula?

  1. 50.00 m
  2. 100.00 m
  3. 200.00 m
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Correct answer: 50.00 m

(speed:10)² : 2 — don't forget the division: (10x10):2 = 50.00 m

Why learners get this wrong: Braking distance = (speed:10) squared, with no further division (so 25 m at 50 km/h, 100 m at 100 km/h).

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On the A35 near Nijverdal you are driving 60 km/h. Per the book formula (speed:10)² : 2, what is your braking distance in metres?

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Correct answer: 18 m

Correct: 18.0 m (±2.0).

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On a provincial road near Wierden you are driving 100 km/h. What is your braking distance per the book formula?

  1. 50.00 m
  2. 100.00 m
  3. 200.00 m
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Correct answer: 50.00 m

Why learners get this wrong: Braking distance = (speed:10) squared, with no further division (so 25 m at 50 km/h, 100 m at 100 km/h).

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In the built-up area of Hellendoorn you explain to a passenger: 'If you accelerate from 50 km/h to 100 km/h, your braking distance becomes exactly 2x as long.'

  1. True
  2. False
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Correct answer: False

Why learners get this wrong: If speed doubles, braking distance also doubles (a linear relationship).

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