ADAC outlines formulas for braking, reaction and stopping distances

The German motoring organisation ADAC explains how to calculate a vehicle’s braking, reaction and total stopping distances. It states that the braking distance grows with the square of speed, using the rule (speed ÷ 10) × (speed ÷ 10) to obtain metres for a normal stop – for example, 25 m at 50 km/h, 100 m at 100 km/h and 225 m at 150 km/h. The reaction distance, covered during the driver’s response time, is added to the braking distance to give the total stopping distance.

For emergency or “hazard” braking, the ADAC notes the braking distance can be roughly halved, giving 12.5 m at 50 km/h, 50 m at 100 km/h and 112.5 m at 150 km/h. Factors such as road slope, brake performance, vehicle load and surface condition also influence the figures.

The guidance distinguishes the terms: braking distance (brake‑to‑stop), reaction distance (perception‑to‑brake) and stopping distance (combined).