Why Stopping Distance Matters
Stopping distance is one of the most important and most misunderstood concepts in driving. Understanding it can save your life — and it is tested on the DMV exam.
Total Stopping Distance = Reaction Distance + Braking Distance
Reaction distance is how far your car travels while your brain processes the danger and your foot moves to the brake. Average reaction time is about 1.5 seconds.
Braking distance is how far your car travels after you press the brake until you come to a complete stop.
Stopping Distance Chart
| Speed | Reaction Distance | Braking Distance | Total Stopping Distance |
|---|---|---|---|
| 20 mph | 22 ft | 24 ft | 46 ft |
| 30 mph | 33 ft | 54 ft | 87 ft |
| 40 mph | 44 ft | 96 ft | 140 ft |
| 50 mph | 55 ft | 146 ft | 201 ft |
| 60 mph | 66 ft | 215 ft | 281 ft |
| 70 mph | 77 ft | 290 ft | 367 ft |
The Key Insight: Speed Squared
When you double your speed, your braking distance increases by four times. This is because kinetic energy increases with the square of speed.
What Affects Stopping Distance?
Several factors increase your stopping distance:
Why This Matters for Following Distance
Your following distance must be long enough to cover your total stopping distance. This is why the recommended following distance increases at higher speeds and in poor conditions.
Practice Stopping Distance Questions
Take a free practice test with reaction time and braking distance questions.