A Gatso is a fixed roadside speed camera that measures the speed of a passing vehicle with radar and photographs its rear. Gatso was the maker's name, and in the UK it has become the everyday word for the roadside box with white lines painted across the carriageway. This guide explains how a Gatso works, what the lines are, why it takes two pictures and how newer fixed cameras differ, using what police forces and the Department for Transport (DfT) publish.
What a Gatso speed camera is
The Police Scotland Safety Cameras website describes Gatso cameras as operating with radar technology and recording two rear-facing images, 0.5 seconds apart. GoSafe, the Welsh road casualty reduction partnership, lists its fixed digital speed cameras under the name Cubic, noting that they were formerly Gatso, and names several Gatsometer models among the equipment it uses. The principle in the roadside housing is the one described below.
Fixed cameras like these suit sites where collisions cluster around one point, as DfT Circular 01/2007, the Department's guidance for England and Wales, puts it. The circular recommends yellow housings, and the overview of the four types of speed camera explains the colour and visibility guidance.
How the radar reads your speed
According to the National Police Chiefs' Council (NPCC) technical guide, an across-the-road radar uses the Doppler effect. The device sends a radar beam across the road at a fixed angle. A beam that meets a vehicle at an angle senses less than its true speed, which the guide calls the cosine effect. Because the angle is known, the electronics correct for it and the speed is read directly without further correction.
Evidence from a prescribed device can be given by certificate, but only if the device is of a type approved by the Secretary of State, under section 20 of the Road Traffic Offenders Act 1988. Police Scotland says its cameras are Home Office type approved and calibrated regularly by a third party.
Why there are two photographs and white lines
Two photographs, half a second apart, show the vehicle in two positions. White lines painted on the road at set intervals appear in both. Police Scotland explains that the markings are used to verify that the speed detected by the radar is consistent with the distance the vehicle travelled between the two photographs, and that the markings do not themselves determine the speed. The radar does.
The NPCC guide adds that the secondary check should normally fall within a band of plus or minus 10% of the radar reading. It is a pass or fail check on the evidence, and if two or more vehicles are in the secondary check area the evidence must show which vehicle caused the reading; if that cannot be told with confidence, the reading should be disregarded.
GoSafe answers the question drivers ask most often. If a vehicle overtaking you or going the other way sets off the camera and you appear in the picture too, the two photographs and the lines show which vehicle travelled further, and so faster.
Gatso compared with newer fixed cameras
Police Scotland describes several fixed systems on one page. The table sets out how they differ.
| System | How it measures | Secondary check |
|---|---|---|
| Gatso | Radar; two rear-facing images 0.5 seconds apart | Check lines painted on the road |
| Vector SR | Tracking radar with multi-lane coverage; infra-red images, no flash | An intelligent virtual grid replaces the lines |
| Redspeed | Loops under the road at traffic lights detect vehicles passing on red; two images, and many units also detect speeding | Staff review the footage |
| HADECS | Calibrated radar on a gantry measures every vehicle; two images | Two images verify the radar speed against distance travelled |
Motorway speed cameras explains the HADECS gantries, and mobile speed cameras covers the units that move between sites.
What follows a Gatso reading
GOV.UK says that within 14 days of the offence you are sent a Notice of Intended Prosecution and a Section 172 notice. The minimum penalty for speeding is a £100 fine and 3 penalty points. GoSafe says fixed and mobile cameras can operate 24 hours a day, and that a missing camera sign does not invalidate an offence.
What BlitzBuddy does with fixed cameras
BlitzBuddy gives no speed camera warnings in the UK, Ireland or other countries outside the five where it warns; your speed, trips and reports from other drivers still work there. In the Netherlands, Belgium, Germany, France and Türkiye, camera warnings switch on by themselves. There, fixed cameras and average speed checks come from OpenStreetMap, Lufop.net and public government lists, and fixed cameras are stored on your phone, so they keep working without signal. In Germany, § 23 (1c) StVO forbids drivers to use a speed camera warner while driving; the warnings can be switched off under Profile, Warnings, and the driver is responsible. In France, article R413-15 of the Code de la route, in paragraph V, has since 5 January 2012 also banned devices that warn of or inform about the location of the equipment used to record traffic offences; using these warnings is the driver's own responsibility. Where speed camera warnings are allowed compares the countries.
More guides on the same topic are collected under speed camera guides.
Sources
- Camera Type, Police Scotland Safety Cameras
- Our cameras, GoSafe
- FAQs, GoSafe
- Guide for the operational use of speed and red-light offence detection technology, version 1.2.1, National Police Chiefs' Council, July 2016 (pdf, linked from National Highways)
- DfT Circular 01/2007: Use of speed and red-light cameras for traffic enforcement, Department for Transport (pdf)
- Road Traffic Offenders Act 1988, section 20, legislation.gov.uk
- Speeding penalties, GOV.UK
- Straßenverkehrs-Ordnung, § 23, Federal Ministry of Justice (in German)
- Code de la route, article R413-15, Légifrance (in French, version in force since 5 January 2012)
- Camera data in the countries where BlitzBuddy warns: © OpenStreetMap contributors
Sources read on 11 October 2026.
Frequently asked questions
What are the white lines near a Gatso camera for?
They are secondary check markings. Police Scotland says they appear in the photographs and verify that the speed the radar detected matches the distance the vehicle travelled between the two images. The radar, not the lines, determines the speed.
Does a Gatso take a picture of the front or the back of the car?
The back. Police Scotland describes Gatso cameras as recording two rear-facing images 0.5 seconds apart.
Can a Gatso mistake which car was speeding?
GoSafe says it can tell which vehicle triggered a fixed camera, because the two photographs are half a second apart and the white lines show which vehicle travelled further, and so faster.
Are Gatsos the only fixed speed cameras?
No. Police Scotland also uses Vector SR cameras, which track vehicles over several lanes and need no road markings. GoSafe lists Gatsometer models under the Cubic name next to Vector SR, Redspeed and other systems.
