A Driver Is Travelling at 90 Mi/h Down a 3% Grade

Stopping distance = reaction altitude + braking altitude

Reaction distance

The reaction distance is the altitude you travel from the betoken of detecting a hazard until you lot begin braking or swerving.

The reaction distance is affected by

• The car'south speed (proportional increment):
  • 2 x higher speed = 2 x longer reaction altitude.
  • 5 x college speed = five 10 longer reaction distance.
• Your reaction time.
  • Normally 0.five–2 seconds.
  • 45–54 twelvemonth-olds have the best reaction time in traffic.
  • eighteen–24 year-olds and those over lx have the same reaction time in traffic. Young people accept sharper senses simply older people accept more experience.

The reaction distance tin can be decreased by

• Anticipation of hazards.
• Preparedness.

The reaction distance tin can be increased by

• The necessity of decision-making (for example, between braking or steering out of the way).
• Alcohol, drugs and medication.
• Tiredness.

Easy method: Calculate the reaction distance

Formula: Remove the last digit in the speed, multiply past the reaction time and and so by 3.

Case of calculation with a speed of 50 km/h and a reaction time of 1 second:

50 km/h ⇒ v
5 * 1 * 3 = 15 metres reaction altitude

More than precise method: Calculate the reaction altitude

Formula: d = (s * r) / 3.6

d = reaction altitude in metres (to be calculated).
s = speed in km/h.
r = reaction fourth dimension in seconds.
3.half-dozen = fixed figure for converting km/h to m/southward.

Example of calculation with a speed of 50 km/h and a reaction time of 1 second:

(50 * ane) / 3.vi = xiii.9 metres reaction distance

Drive slowly or you might non even have time to react to oncoming traffic.

Braking distance

The braking distance is the altitude the car travels from the signal when you start braking until the machine stands still.

The braking distance is affected by

• The vehicle'south speed (quadratic increase; "raised to the power of ii"):
  • 2 x college speed = iv x longer braking distance.
  • 3 x college speed = 9 x longer braking distance.
• The route (gradient and weather).
• The load.
• The brakes (condition, braking engineering science and how many wheels are braking).

Calculate the braking distance

It is very difficult to accomplish reliable calculations of the braking distance as road weather condition and the tyres' grip can vary greatly. The braking distance may for case exist x times longer when there is ice on the road.

Easy method: Calculate the braking distance

Weather condition: Practiced and dry out road weather condition, proficient tyres and good brakes.

Formula: Remove the zero from the speed, multiply the figure by itself and and then multiply by 0.4.

The effigy 0.4 is taken from the fact that the braking distance from 10 km/h in dry road weather is approximately 0.4 metres. This has been calculated past means of researchers measuring the braking distance. Thus, in the simplified formula, we base our calculations on the braking distance at 10 km/h and increase it quadratically with the increase in speed.

Example of calculation with a speed of 10 km/h:

10 km/h ⇒ i
1 * 1 = 1
1 * 0.iv = 0.4 metres braking distance

Example of calculation with a speed of 50 km/h:

l km/h ⇒ 5
5 * 5 = 25
25 * 0.4 = ten metres braking distance

More precise method: Calculate the braking distance

Conditions: Skilful tyres and proficient brakes.

Formula: d = southwardⁱⁱ / (250 * f)

d = braking distance in metres (to exist calculated).
south = speed in km/h.
250 = fixed figure which is always used.
f = coefficient of friction, approx. 0.8 on dry cobblestone and 0.1 on ice.

Case of adding with a speed of 50 km/h on dry out cobblestone:

50² / (250 * 0.8) = 12.5 metres braking altitude

Stopping distance

Stopping distance = reaction distance + braking distance

Calculate the stopping distance with these piece of cake methods

Information technology is summertime and the road is dry out. You are driving at ninety km/h with a automobile with good tyres and brakes. You all of a sudden notice a run a risk on the road and brake forcefully. How long is the stopping distance if your reaction fourth dimension is 1 second?

The stopping altitude is the reaction distance + braking distance. First we calculate the reaction altitude:

• ninety km/h ⇒ 9
• nine * i * 3 = 27 metres reaction altitude

Then nosotros calculate the braking altitude:

• 90 km/h ⇒ 9
• ix * 9 = 81
• 81 * 0.4 = 32 metres braking distance

Now both distances are combined:

• 27 + 32 = metres stopping distance

Important clarification regarding calculations

The different methods provide different answers. Which should I apply?
– Use whichever y'all wish. The differences are so small-scale that they will not impact your theory test, as the margins betwixt the alternatives are quite big.

And so if the alternatives are 10, xx, 40, lx, it does not matter if you become ten metres with one method and 12.five metres with another – both are obviously closest to 10, which is thus the right reply.

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Last updated 2021-01-22.