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When you are studying for a driving test, understanding the theory of stopping distance becomes more than necessary.
Stopping distance theory might look a bit complex on paper and pen, but it is as simple as eating your dinner in reality.
Stopping distance refers to the distance a vehicle travels from the point you think about pressing the brake to until the vehicle stops after pressing the brake.
In the simplest term, stopping distance is the sum total of thinking distance and braking distance.
Let’s explain each of the topics for your better understanding-
What is thinking distance?
Thinking distance refers to the distance that your vehicle travels between when you decide to hit the brake and until you hit the brake.
The term ‘thinking distance’ is also known as reaction distance.
The thinking distance of a vehicle running at the speed of 50mph on a dry road is around 15m or 50 feet.
What is braking distance?
Braking distance refers to the distance that a vehicle travels between the time of hitting the brake and until the vehicle stops.
The thinking distance of a vehicle running at the speed of 50mph on a dry road is around 38m or 125feet.
What is stopping distance?
Stopping distance = thinking distance + braking distance
That means if the thinking distance and braking distance of a vehicle running at the speed of 50mph is around 15m or 50 feet and 38m or 125 feet, the stopping distance would be-
Stopping distance = 15m + 38m or 50feet + 125 feet = 53m or 175meet
In the simplest term, stopping distance refers to the vehicle’s travel from the point the driver thinks about hitting the brake to until the vehicle stops.
If you are a teacher who needs an in-depth discussion on stopping distance, this paper should be a good item that you might want to read.
Average stopping distance
When you drive in a dry and normal road condition, the average stopping distance of a vehicle running at different speed parameters is expectable.
Here is a popular chart that will show you the average stopping distance of a car running at different speed parameters-
Vehicle speed | Thinking Distance (T.D) | Braking Distance (B.D) | Stopping Distance (T.D + B.D) |
20mph | 6m | 6m | 12m (40 feet) |
30mph | 9m | 14m | 23m (75 feet) |
40mph | 12m | 24m | 36m (118 feet) |
50mph | 15m | 38m | 53m (174 feet) |
60mph | 18m | 55m | 73m (240 feet) |
70mph | 21m | 75m | 96m (315 feet) |
Calculating stopping distance
When you will sit for an exam, the reference that I have given above surely would not suffice.
You will have to find out the ways of the calculation so that you can answer any complicated questions.
The following section will describe how you can calculate stopping distance on paper and pen.
For reference, suppose a car is running at a speed of 50km/h.
Now let’s calculate both the thinking distance and braking distance to find out the stopping distance of the car-
Calculating thinking distance
The formula to find out thinking distance is-
T.D = (s x r)/3.6
here,
- T.D = Thinking Distance
- s = Speed in km/h
- r = Reaction time in second
Therefore, the thinking distance of the car is-
(50x1)/3.6 = 13.9m
Calculating the braking distance
The formula to calculate braking distance is-
B. D = s^{2}/250xf
Here,
- B. D = Braking distance
- s = Speed in km/h
- f= Coefficient of friction, which is around 0.8 on a dry road condition and 0.1 on an icy track.
Therefore, the braking distance of the car is-
50^{2}/(250x0.8) = 12.5m
Calculating the stopping distance
Now that we have got the thinking distance and braking distance of the car, let’s calculate the total stopping distance of the car.
The formula to calculate the stopping distance is-
- Stopping distance = Thinking distance + braking distance
= 13.9m + 12.5m =26.4m
To know more about stopping distance, consider checking this extract that has summarized the whole topic in a very organized way.
Shortcut for calculating thinking distance
If a car is running at a speed of 50km/h, the shortcut to calculate the thinking distance is-
- 5x1x3= 15m
Here,
- 5= the single digit that remains after excluding o from the speed of the vehicle, which is 50km/h.
- 1= the reaction time in second
- 3= multiply the previous two numbers by 3 to get the expected thinking distance
Shortcut for calculating the braking distance
If a car is running at a speed of 50km/h, the shortcut to calculate the braking distance is-
- 5x5x0.4 = 10m
Here,
- 5 = the single digit that remains after excluding 0 from the speed of the vehicle, which is 50km/h.
- 5 = You need to multiply the single digit by the same number. In our case, the single digit that we found was 5. Therefore, we are multiplying 5 by 5.
- 0.4 = This is a constant value. While calculating the braking distance, you need to multiply the previous two numbers by 0.4
Now, by summing up 15 and 10, you can easily say that the stopping distance of the vehicle is around 25m.
Shortcut for calculating the stopping distance
Start with 2 and multiply the speed by intervals of 0.5. While the multiplication starts from 2, the speed starts from 20mph.
For example,
- 20mph x 2 = 40 feet
- 30mph x 2.5 = 75 feet
- 40mph x 3 = 120 feet
- 50mph x 3.5 = 175 feet
- 60mph x 4 = 240 feet
- 70mph x 4.5 = 315 feet
To understand how I have calculated the whole thing, this is the ideal paper that you might need to check.
Note:
Remember that the shortcuts mentioned above are only for better remembering or understanding. Following the shortcuts will take you near to the exact value, but may not provide the exact value all the time.
Factors that influence stopping distance
The top four factors that can influence the stopping distance are-
- Weather
- Road condition
- Driver’s physical condition
- And car condition
Weather
Fogg, rain, or snowfall can impact the overall stopping distance.
Foggy weather may create vision errors, which may lead the driver to make a slow decision.
Rainy weather can create hydroplaning, which will always impact badly on decision making.
Snowfall makes the situation even worse.
Road condition
Road condition and weather is highly interconnected. If the tires fail to grab enough friction from the road, no matter how much you know about stopping distance, you will never be able to calculate the exact stopping distance.
Driver’s physical condition
A tired or fatigue driver decides slowly, which may influence the stopping distance.
At the same time, young drivers tend to show aggressive behavior while driving. Such behavior will also influence the overall stopping distance.
Eating or using a mobile phone while driving can also influence the overall stopping distance.
It is all about maintaining defensive driving techniques to keep yourself safe when driving on the road.
Car condition
A faulty brake system of any car reduces the capability of the brake booster, which ultimately will influence the stopping distance even if the driver hits the brake padel at the right time.
Low tire tread depth or zero tire tread depth will also dramatically reduce the stopping distance of a car.