The total stopping distance is your reaction distance plus your braking distance. You calculate them using two formulas: reaction distance = (speed / 10) × 3, and braking distance on dry road = (speed / 10)² / 2. On a wet road surface, this braking distance is approximately one and a half times longer.
1. The Reaction Distance
The reaction time of a healthy, alert driver is on average 1 second: the time between seeing the danger and pressing the brake pedal. The distance you cover in that second is calculated with (speed / 10) × 3.
- At 50 km/h: (50 / 10) × 3 = 15 meters.
- At 120 km/h: (120 / 10) × 3 = 36 meters.
The reaction distance does not change due to the road surface. It only depends on you.
2. The Braking Distance
The braking distance is the distance from the moment the brakes are applied until the vehicle comes to a stop. On dry road surfaces, you calculate this with (speed / 10)² / 2. On a wet road surface, this distance is approximately 1.5 times longer. The condition of your tires (minimum tread depth 1.6 mm) and your brakes also determine how long the braking distance will be.
3. The Total Stopping Distance
Add the reaction distance and the braking distance together, and you have the total distance from seeing the danger to coming to a stop. Important: fatigue, alcohol, or distraction can double your reaction time, significantly increasing the stopping distance.
| Speed | Reaction Distance | Braking Distance (dry) | Braking Distance (wet, ×1.5) |
|---|---|---|---|
| 50 km/h | 15 m | 12.5 m | 18.75 m |
| 90 km/h | 27 m | 40.5 m | 60.75 m |
| 120 km/h | 36 m | 72 m | 108 m |
Frequently Asked Questions
You need to know the distances and be able to estimate them. The questions are often multiple choice with reference values, so the method and the order of magnitude are more important than exact numbers.
No, only the braking distance becomes longer. The reaction distance depends on you, not on the road surface.
1.6 mm.
No Calculation Stress at the Exam Center
Many candidates drop out on stopping distance questions. Mathieu explains with handy mnemonics how to solve these questions within the time limit.
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Last updated: June 2026 · Content verified by Mathieu, instructor · Source: the Belgian Highway Code