How to Challenge a Speed Camera Reading: Attacking the Radar Evidence

In speeding proceedings, the radar reading is the key piece of evidence: a single technical figure decides whether the conduct remains a traffic fine or crosses the line into the road-safety offence of Article 379.1 of the Criminal Code (CP). For that reason, properly challenging that measurement is the most effective line of defence. As criminal defence lawyers specialising in challenging radar readings, in this article we focus exclusively on how the speed-camera evidence is attacked. If what you are looking for is when speeding becomes a crime and what penalties it carries, we explain it in our article on speeding as a criminal offence (Art. 379.1 CP).

The Speed-Measuring Device: Technical Evidence That Can Be Disputed

A speed-measuring device is not an infallible authority but an instrument of measurement subject to a strict legal regime. The speed recorded in the police report is the output of a specific device, used in specific conditions and documented in a particular way. Any of those links may fail, and each failure is a route for the defence.

The key point is that the Article 379.1 CP offence is purely objective: it does not turn on whether the driving was dangerous, but on a figure. And precisely because everything revolves around a figure, the technical reliability of that figure is the real battleground. We systematically review five fronts.

1. The Periodic Verification Certificate

Speed-measuring devices are instruments subject to legal metrological control. This means that, in addition to the initial assessment, they must pass periodic verifications —usually annual— and a further verification whenever the device is repaired or modified. The verification certificate in force is the document proving that, on the date of the measurement, the radar was measuring within its maximum permissible error.

That is why we always request it as the first item in the file. We check:

• That the certificate exists and is produced in the case.
• That it was in force on the day of the capture (an expired verification compromises the validity of the reading).
• That it corresponds to the specific device used (serial number and model), and not to another of the same fleet.

The absence or expiry of the certificate is not a mere formality: it goes to the root of the reliability of the data on which the whole prosecution is built.

2. The Margin of Error by Type of Radar

Metrological rules recognise a maximum permissible error that must be deducted from the reading before the speed is taken as established. That margin is not a single figure: it depends on the type of device and on the conditions of the measurement.

Without going into specific figures —which vary according to the device and the applicable rules— it helps to keep the general logic in mind:

• Fixed radar: installed in a stable location, it usually tolerates the smallest margin of error.
• Mobile radar: operated from a fixed point or from a moving vehicle, its conditions of use (angle, stability) justify a larger margin.
• Average-speed (section) radar: it calculates the average speed between two points from time and distance, which introduces its own particularities in the calculation and its margin.

The margin is usually expressed as a fixed value at low speeds and as a percentage at high speeds. What is decisive is not the exact figure but verifying that the correct margin has been applied to the case. For speeds right in the borderline zone of the offence, applying that deduction correctly may leave the excess below the threshold of Article 379.1 CP and redirect the matter to the administrative route.

3. Signage and the Limit of the Stretch

The excess is not measured against an absolute speed but against the limit in force at the exact point of the road. That is why we verify which limit actually applied there:

• Vertical signage: visibility, validity and consistency of the signs; sections with a temporary reduced limit (roadworks) or a variable one (dynamic panels).
• Transition sections: entries to and exits from urban/interurban roads, where the limit changes and the classification depends on which one applies.
• Nature of the road: the urban/interurban distinction is decisive because it sets different thresholds (excess of more than 60 km/h versus more than 80 km/h).

An error about the applicable limit completely changes the calculation of the excess and, with it, the classification of the facts.

4. The Chain of Custody of the Image

The photograph or video of the capture is the medium linking the measurement to a vehicle and, where applicable, to a driver. Like any documentary evidence, it must offer guarantees of integrity and traceability. We examine:

• That the data associated with the image (date, time, place, speed, identification of the device) are consistent with one another and with the police report.
• That the image shows no alterations or unexplained gaps in its handling from capture to its inclusion in the case.
• That there is correspondence between the image, the verified device and the reading attributed to the person under investigation.

An image whose origin or integrity is not established loses evidential value, however sharp it may appear.

5. Identification of the Driver

Proving the speed is not enough: it must be proven who was driving. The distinction matters because criminal liability is personal, not of the vehicle.

• In automatic captures, the image usually identifies the vehicle clearly, but not always the driver (rear shot, low resolution, several occupants).
• Ownership of the vehicle is not the same as authorship: the owner may not be the one driving.
• The prosecution must prove the identity of the driver beyond reasonable doubt; a well-founded doubt favours the defence.

How We Approach the Challenge

Our way of working starts from the technical documentation, not from impressions. In practice:

• We request the full police report and the verification certificate of the device used.
• We identify the type of device (fixed, mobile or average-speed) and check the margin of error applied to the reading.
• We recalculate the legally relevant speed and compare it with the threshold of the offence.
• We review signage, chain of custody and identification of the driver.
• We assess, where appropriate, the advisability of expert evidence on the device or the measurement.

The settled case law of the Spanish Supreme Court on road-safety offences stresses the objective nature of these offences and the central role of the technical evidence, which reinforces the importance of reviewing the measurement rigorously and from the very first moment.