Approximate Stopping Distances

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Arslaan Asif

The graph shows the approximate stopping distances. It shows thinking distance, braking distance and overall stopping distance.

Stopping distance is the distance the car travels from when the driver sees something to when the vehicle stops, this is called the stopping distance, and this is made up of two parts: the thinking distance and the braking distance.

Stopping distance is calculated by adding together the distance it takes to think and the distance it takes to brake.

Here is the formula to calculate overall stopping distance.

Stopping Distance = Thinking Distance + Braking Distance

The Braking Distance line and the Overall Stopping Distance line on the graph are curves whereas the Thinking Distance line is not. The thinking distance line is straight because the rate of change is consistent this means that the speed which the vehicle is travelling at does not affect the Thinking Distance the thinking distance will stay the same, but the thinking distance will increase as the speed increases because the car will travel further in the same time because it is travelling faster. Doubling the speed will double the thinking distance. E.g. if the vehicle is travelling at 20 mph the thinking distance will be 20 ft. When the line is a curve it means that the rate of change is not consistent, for example if the car is travelling at a speed of 30 mph the thinking distance would be 30 ft and the braking distance would be 45 ft, when you add these together it will give you the overall stopping distance which is 75 ft. this shows that the rate of change is not consistent.

The thinking distance is always the same as the speed you are travelling at. As the speed of the vehicle increases the thinking distance also increases. This is also shown in the graph, at 30 mph the thinking distance is 30 ft this means that the rate of change is consistent; this will give a straight and consistent line which changes as the dependent variable changes. Although the thinking distance is a smaller portion of the overall stopping distance than the braking distance; it is still a huge amount, at 70 mph the thinking distance is 70 ft even before you slam down on the brakes.

The graph shows that the faster the speed of the vehicle the higher the overall stopping distance is, this is because when the vehicle is travelling at 20 mph the braking distance is 20 ft. however when the vehicle is travelling at a higher speed for example at 40 mph the braking distance is 80 ft, this means that as the speed of the vehicle increases the braking distance also increases but not at a consistent rate. Braking distance is not directly proportional to speed whereas the thinking distance is. E.g. when the speed of the vehicle is 30 mph the braking distance is 45 ft whereas when the speed of the vehicle is 60 mph the braking distance massively increases to 180 ft which shows that the rate of change is not consistent.

When you increase the speed of the vehicle from 20 mph to 40 mph the braking distance increases by four times from 20 ft to 80 ft. This is also the same when you increase the speed of the car from 30 mph to 60 mph, the braking distance will increase by a huge distance from 45 ft to 180 ft which is also a increase of four times. The braking distance increases by four times when you double the speed of the vehicle.

The thinking distance is the distance the vehicle travels from when the driver hears or sees something to when the driver responds by applying the breaks. The thinking distance line on the graph is straight; this means that it is a linear relationship. As the speed of the vehicle increases the thinking distance also increases by the same amount for example, if the car is travelling at 20 mph the thinking distance will be 20 ft and when the speed of the car increases to 40 mph the thinking distance is 40 ft. The graph shows that the thinking distance is always the same as the speed of the vehicle.

The overall stopping distance increases as the speed of the vehicle increases. The rate of change is not consistent as shown on the graph, for example when the vehicle is travelling at a speed of 50 mph the overall stopping distance is 175 ft, this is because the thinking distance is 50 ft as it is always the same as the speed, and the braking distance is 125 ft which adds up to 175 ft. As the speed increases to 60 mph the thinking distance becomes 60 ft and the braking distance becomes 180 ft, this adds up to 240 ft. The rate of change is not consistent because as the speed increases the braking distance increases even further, when the speed is doubled the braking distance doesn’t double, it quadruples which means the overall stopping distance is not proportionate to the speed of the vehicle.

Thinking distance is the distance the vehicle travels after the driver has seen or heard something to when the driver actually makes a movement and responds by applying the brakes. Thinking distance increases as speed increases, this is because the thinking distance is directly proportional to speed which means that when the speed changes the thinking distance also changes. Thinking distance depends on the speed the vehicle is travelling at and the reaction time of the driver. The human brain responds quickly but not instantaneously. It may take from 0.2 seconds to over 1 second to respond to something depending on the age and other factors of that person.

The main factor that will affect the thinking distance is the speed the vehicle is travelling at, whatever the speed of the vehicle; the driver will take the same amount of time respond but the faster the car is travelling the further it will go in same amount of time, for example if you double the speed the thinking distance will also double.

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E.g. if the car is moving at 20 mph the thinking distance will be 20 ft and if the speed of the car is doubled to 40 mph the thinking distance will become 40 ft, thinking distance is directly proportional to the speed of the car.

Overall breaking distance can be affected by a number of variables. There are three components to overall stopping distance these are: Mental processing time, Movement time and response time.

Mental Processing Time:

This is the time it takes for the driver to detect something. For example it is the time ...

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