# How to remember stopping distances for the Highway Code

The Highway Code makes you learn this complicated table by rote. But it’s significantly less effort to learn the following formulas:

\[
\begin{aligned}
s(n) &= \text{stopping distance at } 10n \text{ mph} \\
t(n) &= \text{thinking distance at } 10n \text{ mph} \\
b(n) &= \text{braking distance at } 10n \text{ mph} \\
s(n) &= t(n) + b(n) \\
t(n) &= 3n \text{ meters} \\
b(n) &= \frac{3n^2 + n}{2} - 1 \text{ meters} \\
\end{aligned}
\]

Working through one example, stopping at 60 mph:

\[
\begin{aligned}
\text{stopping distance at } 60 \text{ mph} &= s(6) \\
&= t(6) + b(6) \\
&= 18 \text{ meters} + 56 \text{ meters} \\
&= 74 \text{ meters} \\
t(6) &= 3 \times 6 = 18 \text{ meters} \\
b(6) &= \frac{3 \times 6^2 + 6}{2} - 1 = 56 \text{ meters} \\
\end{aligned}
\]

The answer is off by one meter in some cases. But the theory test is multiple-choice, so just pick the answer that’s closest.

Tagged . All content copyright James Fisher 2019. This post is not associated with my employer.