Stopping distance: formula, explanations and clear table

Even when learning for a driver’s license, the stopping distance is an important issue. The question about his calculation is a popular part of the theory test. Finally, on the road, it becomes clear why this is so: if you can’t calculate the stopping distance, you run the risk of not being able to maintain the minimum distance necessary to the car in front of you. Such a situation then holds a great potential for accidents, not only for the unsuspecting person himself, but also for other road users. To make sure you are on the safe side in the future, we have compiled the most important information in our guide.

What is the stopping distance?

How long is the stopping distance at 50 km/h?? We explain the rule of thumb in our guidebook.

Basically, the stopping distance for cars, motorcycles and other vehicles is the distance covered between the recognition of the danger and the final stopping of the vehicle. So far, so good – but if you look at the facts in more detail, it becomes clear that there is more to it than that:

  • Thus, stopping distance is related to the reaction time required for the driver to recognize the hazard, process that information, and physically (d. h. to react to this by applying the brake). On average, this process takes about one second. During the reaction time, a distance is already covered, the so-called reaction distance.
  • The driver then presses on the brake. But the car does not come to a stop immediately. Once again, a distance is covered, the length of which is determined by the speed at which the vehicle is traveling.

It can thus be stated: Braking distance + reaction distance = stopping distance

Rule of thumb for the stopping distance: How the driving school teaches it

Even in driving school, stopping distance is a big topic. The formulas for calculating this may look complicated at first, but are relatively easy to apply once they are understood. In the following we have presented the formulas for you clearly. The stopping distance at 50 km/h and a reaction time of 1 second serves as an example for the calculation.

The rule of thumb for the stopping distance of a vehicle is illustrated here. Please click on the graphic for a larger view.

Comments on the reaction distance

As mentioned, the average reaction time is one second. This can change however fast, if bspw. the driver is distracted, tired or under the influence of alcohol or certain medications. According to the Hessian police, a person’s ability to react can deteriorate by up to 50 percent if he or she has a blood alcohol level of 0.8 per mille.

It is also worth mentioning that the reaction distance is also longer at double speed (100 km/h : 10 = 10 /// 10 x 3 = 30).

Notes on the braking distance

For the stopping distance this is not so simple. If the speed is increased here, the braking distance is increased many times over. If this can be calculated to 25 meters at 50 km/h, it is already 100 meters at 100 km/h (100 : 10 = 10 /// 10 x 10 = 100).

Overall, this has the following consequences: If at a speed of 50 km/h and 1 second reaction time, the stopping distance is 40 meters, then for double the speed: the stopping distance at 100 km/h is 130 meters (30 + 100).

Are there e.g. If there is fog and you only have a visibility of 50 m, the stopping distance is still the same. You should still increase the distance as a precaution.

The stopping distance during emergency braking

A slightly different approach is used for hazard braking. This is an impact braking, so the driver presses the brake pedal, the anti-lock braking system (ABS) ensures that the wheels stop completely and still "jerk" a little further, so that there is the possibility of evasion.

If you do hazard braking correctly, you can divide the stopping distance by two. For the resulting stopping distance, use the rule of thumb for 50 km/h from the example in the graphic.

The braking distance is thus only 12.5 meters long (50 : 10 x 50 : 10 : 2 = 12.5). This gives a stopping distance of 27.5 meters for hazard braking at 50 km/h (15 meters reaction distance + 12.5 meters braking distance = 27.5).

Information on stopping distance is clearly summarized in the table below

Speed in km/hDistance to a stop normally in mDistance to a stop at driving braking in m
10 4 3,5
20 10 8
30 18 13,5
40 28 20
50 40 27,5
60 54 36
70 70 45,5
80 88 56
90 108 67,5
100 130 80
110 154 93,5
120 180 108
130 208 123,5
140 238 140
150 270 157,5

How the stopping distance fits into the formula for the minimum distance

As mentioned, the stopping distance is important in order to be able to correctly maintain the minimum distance to the car in front. Generally speaking, a safety distance of three car lengths or. 15 meters, while out of town the following applies: minimum distance = half speedometer value. If you are not able to keep this minimum distance, it can be assumed that you are committing a misdemeanor according to the list of offenses.

You have a visibility of only 50 m in built-up areas? The stopping distance is greater in poor weather conditions, so you should also increase the distance in the city.

In the context of this, take another look at the stopping distance just described. the rule of thumb for this, notice that this does not quite fit. This is mainly due to the fact that the person in front of you, as soon as he brakes, still covers a stopping distance and does not immediately stop where you first hear his braking.

On the other hand, the fact that in dense urban traffic it is usually impossible to maintain a proper distance of 25 meters (half the speedometer value at a speed of 50 km/h), let alone the stopping distance, is also taken into account in urban areas. At 30 km/h, this would still be 18 meters.

Minimum distance in bad weather conditions

However, these rules of thumb can only be applied in the best conditions – when the road is dry and the sun is shining. Note that ice and wet conditions have a negative effect on stopping distance, visibility when it is poor (such as in precipitation, fog o. darkness), is also a factor that has a negative impact. Therefore, in such cases, the minimum distance should be increased. There is no specific rule of thumb for this, the principle from the Road Traffic Regulations (StVO) applies, § 4 Para. 1:

As a rule, the distance to a vehicle in front must be sufficient to allow the vehicle to stop behind it even if it brakes suddenly.

In principle, of course, the stopping distance is bspw. at 50 m visibility remains unchanged from the time the danger is detected until the car stops, provided the road is dry. Nevertheless, caution should be increased and thus the minimum distance to the vehicle in front doubled if conditions are not ideal.

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