Braking distance and stopping distance: StVO rules of thumb
How to calculate safety-relevant distances
The stopping distance consists of two parts: the reaction distance and the actual braking distance. The reaction distance results from human reaction time (approx. 1 second), during which the vehicle still travels at full speed without braking. The rule of thumb for the reaction distance is: (v/10) × 3, where v is the speed in km/h.
The braking distance under normal braking is calculated as (v/10)², the braking distance under emergency braking as (v/10)² ÷ 2. At 50 km/h this classically results in: reaction distance 15 m + braking distance 25 m = stopping distance 40 m. At 100 km/h the stopping distance rises to 130 m – almost the length of a football pitch. The quadratic relationship shows: double the speed means four times the braking distance.
These rules of thumb apply to dry roads and normal vehicles. In practice, note that: wet roads increase the braking distance by around 50%, and on ice it can increase tenfold. Tire tread, tire pressure and the condition of the braking system also significantly affect the result. The legally required safety distance under § 4 of the German StVO is based on half the speedometer reading as a lower limit, but is often not sufficient in an emergency.