EXPLAINER: How DGT velolaser radars function and the margin they offer speeding drivers

Image of a DGT velolaser. Credit: Twitter@top10motor

Velolaser radars are in use by Spain’s Directorate-General for Traffic (DGT) and are almost imperceptible to drivers.


Velolaser radars are the most lethal of all the cinemometers available to Spain’s Directorate-General for Traffic (DGT) in terms of detecting and penalising speeding motorists. Their technical characteristics and specifications are the reason for their great operability.

They barely measure half a metre, have a very light weight of around two kilos and can work supported on a simple tripod or just placed on a vehicle dashboard or the seat of a motorcycle. Likewise, they can be placed on porticos and other structures, such as guardrails, where they are almost imperceptible to drivers.

Thanks to their battery, the radar devices can work autonomously for almost five hours and, to make matters worse, they can be controlled by WiFi. They are very sensitive, so they work just as well at night as they do during the day and can detect violations in both directions of traffic, although they reach their maximum operability in urban areas.

After a budget of more than €860,000 was approved for their purchase, these radars were tested in 2018 and, since then, there are 60 units spread over the Spanish road system.

The process for imposing a sanction on drivers who exceed the speed limits is the same as when other radars operate, but the scientific basis behind the velolaser is different.

These cinemometers work according to the ‘Doppler effect’, which is basically the frequency changes that sound waves undergo as the source that emits them and the receiver gets closer or further away.

Once the velolaser has detected an excess of speed, it sends the information and the photograph to a nearby device (such as a tablet) to which it is connected via its 4G or 3G connection. This tablet would be in the hands of the Traffic officers, who will be ultimately in charge of drafting and proposing the sanction to the offender.

The police officers do not have to stop the offending driver at that moment. This type of fine can be sent by ordinary mail to the address that appears as the usual address of the owner of the vehicle. If the registered owner was not the one driving the vehicle at the time of the offence, the driver must be identified to avoid additional sanctions.

Normal radars have margins of error. In other words, they have a small margin in the detection of speeding that is regulated in the ITV/2010 Ministerial Order.

The margin of error of a radar is calculated by the slight variation that exists between the real speed at which the car circulates and the one recorded by the device. No matter how precise they are, there is always some deviation or error in the speed measurement.

When applying the margin of error, this small variation is corrected by the DGT so that the measurement is as fair as possible for the driver. Vehicle speedometers do not indicate the precise speed at which a motorist is driving either.

Depending on the type of camera and speed limit, different margins of error apply. For fixed and mobile cinemometers, a margin of 7km is applied in those areas in which it is necessary to circulate at a maximum of 100km/h.

On roads where the limit exceeds 100km/h a margin of 7 per cent of the detected speed is applied. In the case of helicopters and section radars, the margin of error is always set at 10 per cent of the detected speed.

Velolaser radars, however, have a smaller margin of error than normal radars. According to a ruling by the Supreme Court, the figure enforced for them is 5 per cent, that is, 5km above the speed detected, as reported by 20minutos.es.


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Written by

Chris King

Originally from Wales, Chris spent years on the Costa del Sol before moving to the Algarve where he is a web reporter for The Euro Weekly News covering international and Spanish national news. Got a news story you want to share? Then get in touch at editorial@euroweeklynews.com