**The margin of error of a system is the maximum error that can be assumed in the measurement it performs**understanding that the device cannot guarantee 100% accuracy and therefore cannot perform a perfect measurement. Although this term is applied to many different areas, especially statistics, today we continue with a somewhat controversial topic, that of **radar margin of error** and other margins that intervene in the identification of speeding.

## What is the margin of error?

As we said, the margin of error is the maximum error that can be assumed in the measurement. The **margin of error of a kinemometer, of a radar**, is therefore the maximum error that can be incurred when identifying the speed of a vehicle. That margin of error or tolerance is set by law. In any case, **there is a second margin of error**, even more important for the driver, **the one applied by Traffic**, which is what is taken into consideration when penalizing a driver for speeding.

Finally also **there is a third margin of error that comes into play in speeding, that of the speedometer**.

## The evolution of traffic error margins

We have been warning you for some time that relying on the margin of error that we have long considered assumed by the radars in charge of pursuing speeding was, at the very least, a great risk of being sanctioned. Years ago, the DGT itself established at least a margin of error, by excess, of 10% to consider that a driver had committed an offense.

Later, the maximum margin of error allowed for the kinemometer, depending on its nature, was taken into consideration. At that time, a margin of error of 5% began to be applied in fixed installations and 7% in mobile radar installations.

But for a while now the situation has changed and **Knowing how these margins of error work, and distrusting them, can save us some unpleasant surprise, some fine for speeding**. In 2015, the error margins applied were unified taking into account the 7% applied to mobile installations. Now, what are these margins of error?

As no measurement system is infallible, there is always a maximum margin of error allowed for radars, but the approved margin of error, which is considered when processing fines, varies depending on the device used.

## 1. The margin of error of the kinemometer, of the speed radar

**No measurement system is foolproof**, there will always be a margin of error, no matter how small, below which it cannot be guaranteed that a vehicle will exceed the speed limit. In other words, it can only be stated that a vehicle exceeded the maximum allowed speed, if the speed that it identified in the kinemometer is higher than the speed limit of the road, plus the margin of error stipulated for the measuring device.

The measuring devices in **fixed installations** used by the General Directorate of Traffic have a **maximum permissible margin of error**, and I repeat, maximum, of 5 km / h for speeds lower or equal to 100 km / h and 5% for speeds higher than 100 km / h (according to order ITC / 3123/2010). That would mean that on a road limited to 120 km / h, any fixed radar would be able to affirm, with complete rigor according to the law and its homologation, that a car detected at at least 126 km / h would have exceeded the maximum speed allowed. And I repeat that we are talking about maximum margins. Obviously there are even more effective kinemometers, with a much lower margin of error than the 5% stipulated in the Traffic action protocol.

In the case of **mobile installations**, the **maximum margin of error of the device** It must not exceed 7 km / h at speeds lower than or equal to 100 km / h. And it must not exceed 7% at speeds above 100 km / h. The maximum margin of error for medium speed kinemometers is 5%.

In any case, we would always be talking about **kinemometers homologated and periodically verified** following the service conditions recommended by its manufacturer. Traffic is responsible for ensuring the correct functioning of the measuring devices, which must always be identified by a unique serial number, which will also appear in the communication received by the offender.

The margin of error of kinemometers is getting smaller and smaller. Exceeding the speed limit of the road by 1 km / h may be more than enough reason for us to receive a sanction

## 2. The margin of error considered by Traffic

Until a few years ago Traffic, and each provincial Traffic Headquarters, had a specific protocol to consider the minimum margin of error that determines an excess of speed. But those margins have been narrowing more and more in recent years. I am sure that more than one reader will have received in recent years some penalty for speeding on roads limited to 120 km / h for traveling at 130 km / h, even for traveling at lower speeds. But hadn’t we agreed that there was a 10% margin of error? Here is the reason why that margin has become obsolete.

The problem we face, therefore, is that **Traffic has stopped considering in most of the headquarters that margin of error considered until a few years ago**. On the other hand, in 2015 the DGT decided to unify the maximum margin of error established for kinemometers and apply it generally. Thus, regardless of the nature of the kinemometer and its location, the margin of error considered by Traffic must be the same.

So things, **The margin of error established by Traffic is 7 km / h for maximum speed limits lower than 100 km / h and 7% for higher maximum speeds**We insist, regardless of the section and the radar used.

## 3. The margin of error of the car speedometer

On the other hand we have to bear in mind that **the speedometers in the cars we drive already have an even greater margin of error from the factory**. Unless we have made major modifications without correcting the speedometer – for example, a change in the tire measurement with respect to the standard used – the usual thing is that the speed that the speedometer shows us is higher than the real speed at which we circulate. That is, theoretically, since the speedometer error between different manufacturers and models can also vary significantly, when our speedometer tells us that we are driving at 121 km / h, it is likely that the speed at which we are driving is less than 120 km / h .

**Are we to trust the error of our speedometer?** Each driver will be aware of the error that, to a lesser or greater extent, the speedometer of his car offers. But, once again, playing with those margins, worth the redundancy, can also play a trick on us.

Generally the speedometer of our car will also have a more or less marked error in its measurement, downward. So we will circulate at a lower speed than the one indicated. That margin of error can vary greatly depending on the manufacturer, model and even the specifications of the car.

And as a personal consideration I would like to say that, even more important than the precaution not to trust ourselves with the error margins that we considered years ago, the fact of driving calmly and without fear that traveling at 120 km / h on the highway, kilometer per hour up, kilometer per hour down, let’s think we can get a ticket home. AND **I say this referring, above all, to those who tend to brake abruptly when passing under a gantry with a fixed radar**. Because deep down that obsession with avoiding fines can cost us a greater upset, an accident, for example.