Reaction path: seeing, recognizing and reacting also takes time

"How do I calculate the reaction distance and what a formula is necessary?"

How do you actually calculate the reaction distance?

How do you actually calculate the reaction distance?

Every driver’s license candidate faces numerous calculations and formulas in driving school. One of the most important is the Stopping distance – the distance the vehicle needs to travel from the appearance of an obstacle to a complete stop. This is made up of the braking distance and the reaction distance.

While the braking distance describes the distance the car travels during the actual braking process, at least in theory, the Reaction path to the Calculation activity of the brain of every motor vehicle driver bound. When a driver perceives an obstacle, this information must be processed by his control center and converted into a reaction. This takes some time, though not much. In this time the car also covers a certain distance, the reaction distance.

But how exactly can you change the reaction path at the car calculate? Which factors can influence the reaction pathway affect? You can find out this and more below.

Reaction distance in m ≈ (speed ÷ 10) x 3

FAQ: Reaction distance

The formula needed to calculate the reaction distance is as follows:
(speed in km/h ÷ 10) x 3* = reaction distance in meters
* one second is assumed here as reaction time

An overview of the reaction distances at speeds between 10 and 200 km/h can be found in this reaction distance table.

Distractions in particular can have a negative effect on the reaction distance. However, alcohol and drugs behind the wheel can also limit the ability to react. An overview of the factors that can influence the reaction distance can be found here.

This is how the calculation of the reaction distance works for cars, trucks, etc.

Mandatory program in driving school: without calculation from the reaction distance, the driver's license is far away

Mandatory program in driving school: without calculation from the reaction distance, the driver’s license is far away.

The reaction distance describes per Definition the distance the vehicle travels in the time it takes the driver to see an obstacle that appears registers, the brain the data processes and a corresponding Reaction triggers. In relation to the stopping distance of a motor vehicle, the reaction is the Application of the brake to be seen by the driver.

From this moment the braking distance. Depending on Speed but the distance covered during the reaction time is sometimes considerable – and so is the stopping distance actually required at the end.

In the Driving school the reaction distance is on the agenda because it is precisely here that the Sensitization of the new driver is important.

In order for novice drivers to assess how significant this distance traveled is, they are given in driving school a simplified reaction distance formula given to the hand.

Together with the braking distance, the reaction distance is part of the stopping distance of a vehicle.

With this Formula you can calculate the reaction distance:

Reaction distance in m ≈ (speed ÷ 10) x 3

For this reaction distance calculation, it is assumed that the driver’s maximum reaction time is approximately one second is. In combination with the braking distance, this also results in the Stopping distance of a motor vehicle.

The curved equals sign means that these are only approximate values when you calculate stopping distance, reaction distance and braking distance in driving school.

Form calculations theoretical basics, but are not always one-to-one transferable to practice.

Reaction distance + stopping distance: Driving schools usually offer simplified formulas

Reaction distance + braking distance: the driving school usually offers simplified formulas.

Empirically (experiential science) shows that numerous factors influence reaction distance and braking distance. These are not taken into account in the simplified formulas that novice drivers and others are confronted with, but are always thought of here under ideal conditions. Calculations beyond this are part of physical and complex mathematical considerations.

Before we look at what influences can act on the reaction distance, some Calculation examples serve as an illustration.

Afterwards, we will also give you a table in which we have already carried out the calculation of the reaction distance for speeds up to 200 km/h.

How long is the reaction distance at 30 km/h?

To calculate the distance traveled by the vehicle during the reaction time at a driven Speed of 30 km/h To calculate the braking distance, we use the above formula again and insert the kilometers per hour. case-related, this results in the following calculation:

Reaction distance ≈ (30 ÷ 10) x 3
Reaction distance ≈ 9 meters

At a speed of 30 km/h, the driver and his car thus cover a distance of approximately 9 meters in the assumed maximum reaction time of about one second back before the braking begins. The perception of an obstacle is only followed by the application of the brake after about 9 meters. Together with the subsequent braking distance, this results in the total stopping distance actually required in the end.

The formula for calculating the reaction distance assumes ideal conditions

The formula for the calculation of the reaction distance assumes ideal conditions.

In the following Examples we want to limit ourselves to the pure calculation of the reaction distance and save extensive explanations and superfluous repetitions.

How long is the reaction distance at 50 km/h?

Reaction distance ≈ (50 ÷ 10) x 3
Reaction distance ≈ 15 meters

How long is the reaction distance at 60 km/h?

Reaction distance ≈ (60 ÷ 10) x 3
Reaction distance ≈ 18 meters

How long is the reaction distance at 80 km/h?

Reaction distance ≈ (80 ÷ 10) x 3
Reaction distance ≈ 24 meters

How long is the reaction distance at 100 km/h?

Reaction distance ≈ (100 ÷ 10) x 3
Reaction distance ≈ 30 meters

Tabular overview of the reaction distance up to 200 km/h

Driving speed in km/h Re-action distance in m
10 3
20 6
30 9
40 12
50 15
60 18
70 21
80 24
90 27
100 30
110 33
120 36
130 39
140 42
150 45
160 48
170 51
180 54
190 57
200 60

Which aspects influence the reaction path?

Both reaction distance and braking distance are influenced by different factors

Both reaction distance and braking distance are influenced by different factors.

As already alluded to several times, there are numerous factors that can influence both reaction and braking distance. While technical aspects such as tire and vehicle condition are of primary importance in the latter in the reaction distance, the physical and mental state of the respective driver is important. The human factor therefore plays an essential role here, not technology.

The following are some processes and constraints that can have a significant effect on reaction time, and therefore, in the end, reaction distance have a negative influence:


The reaction time of about one second is an ideal mathematical construct. Although it largely corresponds to human capabilities, brain performance differs from person to person and also conditionally. Fatigue, for example, causes the brain cannot process incoming signals correctly or normally. Registering, processing and reacting are delayed. Overtiredness can thus lead to Reaction delay which – if it hits the driver – also leads to an extension of the reaction distance.

This means that not only the risk of microsleep, which can occur in the worst case due to overtiredness, is a major accident risk, but also general fatigue. The slowed reaction time prolongs the reaction pathway in case of emergency and can thus contribute to the collision in case of doubt.


However, it is not only physical changes that can exert a significant influence. Driver inattention remains particularly dangerous in road traffic. Distractions there are many. However, whether it’s the cell phone at the wheel, adjusting the radio or navigation system, eating, drinking, smoking or talking: all processes that distract the driver from what’s happening on the road can Extend reaction distance.

The reason for this is, first of all, that the distraction causes a Traffic obstruction either seen too late or not initially recognized as such because the brain is still busy processing other data. reaction is then delayed, the stopping distance is longer and, in case of doubt, the Rear-end collision pre-programmed.

Constant caution and consideration in road traffic are thus comprehensibly laid down as the foremost principles in § 1 Paragraph 1 of the German Road Traffic Regulations (StVO).

Alcohol and other drugs

Consumption of alcohol before driving can have a negative influence on the reaction path

The consumption of alcohol before driving can negatively influence the reaction pathway.

Everyone is aware that intoxicants of any kind also have an influence on the Perception of the consumer. However, many people underestimate how quickly alcohol can become a danger behind the wheel. Even small amounts namely change the transmission of information in the brain.

How alcohol works?

  • Even at low blood alcohol concentrations of around 0.2 per mille, those affected can Distances can no longer be estimated accurately. This has fatal effects, especially in road traffic – also on the reaction pathway. A misjudgement of the proximity of a suddenly appearing obstacle can lead to a wrong decision: Instead of the necessary emergency braking, for example, only normal braking takes place and an accident occurs.
  • With increasing alcohol concentration also reduces the user’s field of vision of the consumer. When driving a car, a restricted field of vision of the driver means that possible obstacles outside it can no longer be perceived in time.
  • Motor failures are also affected by alcohol consumption – the body no longer fully obeys the commands of the brain, which makes it more difficult to translate the information into an adequate reaction.
  • In principle, alcohol also reduces the Reactivity, because the ethanol in the blood slows down the transmission of data and impulses between the neurons in the brain.

Alcohol thus has a significant influence on all three areas of reaction time: seeing, recognizing and reacting.


The reaction pathway can also be negatively affected by legal drugs

The reaction path can also be negatively affected by legal drugs.

Similar to alcohol and other intoxicants Medications can also influence the ability to react. For example, even simple antihistamines (allergy medications) often have a fatiguing effect and can thus influence the reaction time in road traffic – this is another reason why they should usually be taken before going to bed. On the other hand, these drugs reduce the effects of overreactions to pollen, for example, which even the Restricting driving ability can.

With most medicines, which can have a similar effect, appropriate Contraindications in the package insert listed. For this reason, you should always read it carefully to ensure that the medication does not end up being dangerous for you and other road users.

If an accident occurs because you were under the influence of medication, you could at least be given a Partial blame for the damaging event be assigned.

According to the German Road Safety Council About five percent of all medications approved in Germany have a negative effect on driving ability. Of particular concern are sedatives, sleeping pills and painkillers, but also cardiac medication, high blood pressure drugs and psychotropic drugs.


Also health problems can influence the reaction time and thus the reaction path in road traffic. The possibilities here are numerous and range from congenital mental limitations to mental illnesses to physically caused deficits, for example after a stroke.

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