speed camera sign in a 30mph zone

Explained: How do speed cameras work?

Getting caught speeding is one of the most frustrating things that can happen when behind the wheel, and also one of the easiest penalties to fall foul of. There’s nothing worse than seeing a speed camera that little bit too late and just waiting, knowing that sooner or later, that little brown envelope from the DVLA will be falling through your letterbox. Luckily, Scrap Car Comparison is on hand to provide you with everything you need to know about speed cameras, what they look like, how they work and how to avoid being caught.

Yorkshire, UK: May 8, 2004: Cars passing yellow Gatso road traffic speed camera

How do regular speed cameras work? 

The most common type of speed camera you’re likely to encounter when on the road is a Gatsometer camera, which have been frustrating British drivers for over 30 years. Gatsos, as they’re often referred to, are almost impossible to miss. Like all speed cameras in the UK, they are legally required to be painted bright yellow, and with their large boxy design, stick out like a sore thumb when put up against the typical green backdrop of the British countryside. You’ll also often have road signs warning you of the fact that they’re there, so there’s rarely an excuse to say you didn’t see one coming. 

A rear-facing camera, the Gatso will record you speeding after you’ve passed the camera, and even if there are road markings on either side of the road, it can only record the speed of someone going in the direction that it’s pointing. If you’re wondering why the road markings are there, well, that’s how it catches you. The camera will take two photos in quick succession, and using the lines on the road as a reference, can prove if you were driving over the speed limit.


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How do average speed cameras work?

Average speed cameras are most commonly found on motorways, and are often greeted with a groan as you see the matrix sign read “AVERAGE SPEED CHECKS”. Often you’ll find drivers braking every time they come up to one of the cameras, or jumping between lanes to try and outsmart them – but how do they work?

A minimum of two cameras, this time built by SPECS rather than the Gatso we’ve already spoken about, will be set up along a stretch of road and will use automatic number plate recognition (ANPR) to monitor how long it takes you to get from one camera to the other, working out your average speed throughout the journey. The first camera in the sequence will take an infrared snap of your car as it goes along, while the second (and further) will take a pair of photos, another in infrared and one in colour. The cameras will also store the time in which the photos were taken, which an onboard computer will use to calculate how long it took to get from A to B. 

By using the timecode of both photos, the computer can work out just how fast you were going between the two cameras, meaning that just anchoring on to go past the actual unit itself isn’t going to do you any favours at all. As the name suggests, the camera works out the average speed, so if the limit is set at 50 and you do 60 for the vast majority between cameras, only slowing down to 50 for the gantries themselves, you’re going to be averaging much closer to 60 than you are 50.

Another tactic that people often try to use to escape from average speed checks is to hop from lane to lane, thinking that the camera won’t be able to work out the fact that they’ve switched lanes. This is a risky move to make, as often average speed cameras can be set to overlap with one another, so you’re never fully sure which ones have snapped you before changing lanes.

Like the Gatso cameras, these cameras are relatively easy to spot when going along a motorway, and are often there during roadworks or newly completed “Smart” motorways. On the side of the road you’ll see a bright yellow frame holding two cameras that look a little like an external CCTV camera. This is a SPECS system and will be used when an average speed check is in force. Occasionally these will remain up after or before roadworks take place, and will inform road users by a physical road sign underneath them that they’re currently not in use.

Do all speed cameras flash? 

It’s a common misconception that you’re going to get away with it if you drive past a speed camera and it hasn’t flashed. Not all cameras use a flash when taking the photo, and sometimes if you’re caught in the middle of summer on a bright sunny day, the flash will not be needed anyway.


Front-facing cameras, such as a Truvelo Combi camera, often use a filter rather than a flash to avoid dazzling the oncoming speeding driver, while speed guns, used by police and traffic safety officers, use radar and laser technology to clock how fast you’re going, both of which are invisible to the naked eye. 

Can speeding cameras be wrong? 

It’s a well known fact that, occasionally, technology can go wrong. However, in the case of a speed camera, unless you can prove that you were not driving above the limit when snapped, you’re going to have a very, very hard time arguing your case. Most cameras nationwide are activated when a car goes past the camera at 10% of the limit plus an extra 2mph – that’s 35 in a 30, or 79 on the motorway. However, this isn’t always the case so to be absolutely sure, just stick to the limit.

If you are certain that you’ve remained under the limit and been given an erroneous fine, you’ll have to be able to provide the evidence to back you up, which will usually mean gaining the photo from the camera itself – not an easy task given you’ll be asking the very people your arguing against to provide you with the photo. 

Do all police cars have speed cameras? 

You might think that, logically, all police cars have a speed camera somewhere within the car, but that isn’t always the case. Officers will regularly carry speed guns with them, often parking up in a layby somewhere to try and catch motorists pushing themselves that little too much. Police cars are also fitted with onboard cameras, and if they’re following you (or chasing if you’re brave/stupid enough to try and run away) they will be able to clock your speed as a result.

Do mobile speed cameras have to put signs out? 

Legally there is no requirement for a mobile speed camera to let you know that it’s there. It could even be disguised as any old van and it still wouldn’t be breaking any rules. However, most mobile speed cameras will place themselves in easy to spot locations, and will not hide the fact that they’re in operation. Contrary to popular belief and scepticism, cameras aren’t there to catch you out and make a quick bit of cash for the Government, and many traffic officers would feel that if they get to the end of a shift without having to report a single driver over the limit, then it’s been a successful day at the office.

Motion blur on vehicle as it passes forty miles per hour sign

How do you know if you were caught by a speed camera? 

As already mentioned further up this page, not all speed cameras flash, and even if you do see a speed camera flash, there’s still no guarantee that it’s you that’s been snapped by the camera. There’s only one way to be certain that you’ve fallen foul of a speeding camera, and that’s when a letter from the DVLA falls through your letterbox.

Is there a way to know where speed cameras will be? 

A strategically placed mobile camera unit could even catch out the most cautious of drivers. Luckily there are ways that you can keep your wits about you thanks to the advancement in mobile technology helping keep drivers alert at all times. 

There are a wide range of standalone units alongside an even greater range of mobile apps offering drivers more information than they have ever had behind the wheel. Not only can these apps warn you of upcoming permanent cameras, but often have temporary cameras listed when reported by its users. Even if the camera isn’t there anymore, it will at least warn you of a potential hotspot – which is usually where mobile cameras will be located. 

For more information on how to keep you and your car on the road for as long as possible, and as safely as possible visit our Car Care hub to find more hints and tips on everything from how to fly through your lessons to keeping your car in top-notch condition with our wide range maintenance guides.

If your car is looking like it’s seen better days, or is simply nearing the end of its usable life, Scrap Car Comparison is able to get you the very best deal in the quickest way. Using our nationwide network of Scrap and Salvage specialists, we’re able to arrange a collection for your car, no matter where you are, and it won’t cost you a penny. Get a guaranteed quote today and find out just how much your car could be worth.

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