Stopping Distance

The stopping distance is the distance travelled by the car between the moment when you discover a danger and when the car is completely still. The stopping distance is generally divided into two distinct parts; reaction distance and braking distance. Stopping distance = reaction distance + braking distance.

Reaction Distance

The reaction distance is the distance travelled by the car between the moment when you have noticed the danger and when you begin to apply the brakes. The reaction distance is affected by two factors:

Reaction time

There are several factors that affect your reaction time. Your reaction time will be shorter if you are an experienced driver and prepared to act. However, the effects of alcohol, drugs and tiredness can make your reaction time longer.

Speed

The reaction distance changes in proportion to speed:

2 times the speed => reaction distance is 2 times as long

4 times the speed => reaction distance is 4 times as long

A simple method for calculating your approximate reaction distance with one second reaction time:

Delete the 0 from your speed and then multiply by 3.

Example:

50 km/h: 5 x 3 => 15 metres

70 km/h: 7 x 3 => 21 metres

Table using this method:

Km/h = reaction distance (metres)

30 => 9

50 => 15

60 => 18

70 => 21

90 => 27

110 => 33

Braking Distance

Braking distance is the distance between when you begin braking and when your car has come to a complete stop.

Factors which affect the braking distance:

• Road conditions: The best road condition, which result in the shortest braking distance, is dry asphalt. If the road conditions are slippery, then the braking distance will be longer.
• Tyre traction: If the tyres are worn, they will have poor traction and the braking distance will be longer.
• The brakes: The type of brakes and their condition will also affect the braking distance. Most cars have so-called ABS brakes, which shorten the braking distance on most surfaces.
• Weight: The heavier the load or the more the car weighs, the longer the braking distance will be.
• Slope: If the road has an upward slope then the braking distance will be shorter and if it has a downward slope then it will be longer.

• Speed: The higher your speed, the longer the braking distance. Braking distance increases quadratically with speed:

2 times the speed => 4 times the braking distance

3 times the speed => 9 times the braking distance

A method for calculating the approximate braking distance:

Delete the 0 from the speed. Multiply the number by itself and then multiply by 0.4. This formula assumes that the car has good brakes, good tyres, and is driven on dry asphalt.

Example:

30 km/h: 3 x 3 x 0.4 = 3.6 metres

50 km/h: 5 x 5 x 0.4 = 10 metres

Table using this method:

Km/h => braking distance (metres)

30 => 3.6

50 => 10

60 => 14.4

70 => 19.6

90 => 32.4

110 => 48.4

Calculating Your Stopping Distance

To calculate your stopping distance, use the methods above and add the two values together.

Example at 50 km/h:

Reaction distance + Braking distance = Stopping distance

(5 x 3) + (5 x 5 x 0,4) = 15 + 10 = 25 metres

Table for stopping distance:

Km/h => Stopping distance (metres)

30 => 12.6

50 => 25

60 => 32.4

70 => 40.6

90 => 59.4

110 => 81.4

From km/h (Kilometres Per Hour) to m/s (Metres Per Second)

It may sometimes be necessary to convert km/h to m/s in order to calculate how far the car will travel during a number of seconds. If, for example, you close your eyes for one second or reach for your mobile phone during two seconds; how far will the car travel during this period of time? If, for example, you are travelling at 15 m/s and you take two seconds to reach for your mobile phone, then you will travel 30 metres (2 x 15 = 30) during that period of time.

Simple calculation

When you convert km/h into m/s, you can make an estimation, as it is difficult to make an exact calculation without a calculator.

Begin by deleting the zero from your km/h and then multiply by 3. Example, calculation of 30 km/h to m/s:

Delete the zero from the km/h: 30 => 3

Multiply by 3: 3 x 3 = 9

Using this estimation, you can therefore say that 30 km/h is approximately 9 m/s.

Exact calculation

To make an exact calculation, divide the km/h by 3.6. Example, calculation of 30 km/h to m/s:

30 / 3.6 = 8.33333...

With this calculation, you can therefore say that 30 km/h is exactly 8.333 m/s.