On a dry road with a 1.5-second reaction time, a car needs about 33 m to stop from 50 km/h and 91 m from 100 km/h.
- Reaction distance (m)
- Braking distance (m)
| Speed (km/h) | Reaction distance (m) | Braking distance (m) | Stopping distance (m) |
|---|---|---|---|
| 20 | 8.3 | 2.0 | 10.3 |
| 30 | 12.5 | 4.4 | 16.9 |
| 40 | 16.7 | 7.9 | 24.5 |
| 50 | 20.8 | 12.3 | 33.1 |
| 60 | 25.0 | 17.7 | 42.7 |
| 70 | 29.2 | 24.1 | 53.3 |
| 80 | 33.3 | 31.5 | 64.8 |
| 90 | 37.5 | 39.8 | 77.3 |
| 100 | 41.7 | 49.2 | 90.8 |
| 110 | 45.8 | 59.5 | 105.3 |
| 120 | 50.0 | 70.8 | 120.8 |
| 130 | 54.2 | 83.1 | 137.3 |
How it is computed
Reaction distance = speed (m/s) × reaction time. Braking distance = speed² ÷ (2 × μ × g), with a dry-asphalt friction coefficient μ = 0.8 and g = 9.81 m/s². Stopping distance is the sum. Doubling the speed multiplies the braking distance by four.
FAQ
How much longer is it on a wet road?+
Wet asphalt has a friction coefficient around 0.5, which makes the braking distance about 60% longer; on snow or ice it can be several times longer.
What reaction time should I use?+
1.5 seconds is a common planning value for an alert driver. Fatigue, distraction or an unexpected hazard can push it past 2 seconds.