Unlike thinking distances, braking distances are not directly proportional to speed. A slight increase in speed greatly increases braking distances. This is why there is a continuous campaign to enforce the 30 mph speed limit in built-up areas.
|Speed (mph)||Speed (m/s)||Braking Distance (m)
Looking carefully at the data, we can see that doubling the speed (from say 20 to 40 mph) increases the braking distance by four times (6 to 24 m). Doubling from 30 to 60 mph has the same effect: braking increases 4 times from 14 to 56 m.