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When learning for your theory exam, you come across many different terms. Some seem quite similar to each other, while they still mean something different. A number of concepts that many people get confused about are: reaction time, braking distance and stopping distance. These are important concepts that often come back on the theory exam. It's also important later in practice to be able to participate safely in traffic. That's why I'm going to help you by clearly explaining what the difference between these concepts is. I'll also tell you how the associated formulas work and give you some handy tips.
The reaction time is the time you need to react to an unexpected situation in traffic. So the moment between seeing and acting. Suppose: a playing child unexpectedly runs onto the road. You have to process that first and only then react by stepping on the brake. During that time, the car just keeps driving.
On average, the reaction time lasts about 1 second for a rested or concentrated driver. For an experienced or alert driver, this can even be faster, namely 0.7-0.8 seconds. Drivers who are tired, distracted, stressed or under the influence of alcohol or drugs have on average a doubled reaction time of 2 seconds or more.
So it's important to know that the circumstances in which you drive can have a lot of influence on the reaction time!
Calculation rule:
Distance during reaction time = speed (m/s) × time (s).
Example:
You're driving 80 km/h = about 22 meters per second. Your reaction time = 1 second. Distance in that second = 22 × 1 = 22 meters.
Even before you step on the brake, you've already driven the length of a large coach further.
The braking distance is the distance your car needs from the moment you brake until you come to a complete stop.
Calculation rule:
Braking distance = (speed / 10)² ÷ 2
Steps:
Divide the speed by 10: At 50 km/h this is 50/10 = 5
Square the result: 5×5 = 25
Divide the result by 2: 25/2 = 12.5 meters
Note: This is the ideal calculation for a dry road surface with optimal brakes and tires. In practice, this can be different due to factors such as road surface, tires and weather conditions. In the rain it can increase significantly and in slippery conditions even double or triple!
The stopping distance is the total distance you need to come to a stop. This is from the moment you notice something until the moment your car is really stopped. So: reaction time + braking distance.
Calculation rule:
Stopping distance = (speed in m/s × reaction time) + ((speed / 10)² ÷ 2)
So you add the meters you cover before you even start braking to the meters you need to come to a stop.
Example at 100 km/h:
Reaction distance: 100 km/h = 28 m/s = 28 meters
Braking distance: (100/10)²/2 = 50 meters
Stopping distance: 28 + 50 = 78 meters
Example at 30 km/h:
Reaction distance: 30 km/h = about 8.3 m/s (round to 8 meters)
Braking distance: (30/10)²/2 = 4.5 meters (round to 5 meters)
Stopping distance: 8 + 5 = 13 meters
Now that you know the difference between reaction time, braking distance and stopping distance, let me show you some questions that regularly come back in the theory exam.
"You're driving 50 km/h. Your reaction time is 1 second. What is your stopping distance?"
Reaction distance: 14 meters
Braking distance: 12.5 meters
Total: 27 meters
"What belongs to the stopping distance?"
Only the braking distance
Only the reaction time
Reaction distance + braking distance
Only the following distance
Sometimes they use clever trick questions:
"You're driving 70 km/h. How large is the braking distance?"
Many students then accidentally calculate the stopping distance. So always read carefully what's being asked!
Read each question carefully: many mistakes arise because you read too quickly or due to the feeling of time pressure. So look carefully whether it's asking about reaction time, braking distance or stopping distance.
Learn the rules of thumb well: once the calculations are in your head, almost nothing can go wrong!
Practice: the more often you practice the calculations, the faster you can make them. This way you also learn the different question types at the same time.
Stay calm: Do you see a difficult calculation question? Skip it if necessary and come back to it later. This way you can first clear your head and look at it again later.
Use memory aids: stopping distance = see – think – brake – stop.
At 50 km/h you need about 27 meters and at 100 km/h over 78 meters.
Now that you know what these three different concepts mean, you can go into the theory exam with much more peace of mind. Reaction time, braking distance and stopping distance may seem like dry calculations, but in practice they definitely make the difference between stopping in time or causing a collision. Always remember: the better you understand the theory, the more relaxed you'll be in the car later. So go for it, practice those exam questions and make sure you confidently get your license!
