Police Speed Traps

Radar Detectors

As the radar signals given off by Gatso cameras are very weak, a radar detector will need a line of sight of the road ahead to give you the best performance in detecting these signals and therefore give you the maximum warning range before the camera location. Gatso cameras are rear-facing and point away from you, looking out towards the direction of your travel.

The radar signals they emit bounce off the road, trees and other street furniture around and therefore also scatters in your direction, which is how you get your advanced reading. If you have a busy road with cars in front of you or many cars on the other side of the road they will help bounce the signal back to you.

Sometimes Gatso camera can be set up as temporary portable cameras, sometimes called Mini Gatso Cameras, at places like motorway roadworks, so look out for alerts from these too. If you pass a Gatso camera and do not get any alerts, it is either a dummy box at the side of the road to slow people down or that the unit has run out of film and is temporarily switched off.

Radar waves are also used by various other traffic management systems, most notably pedestrian crossing monitors so you will also get advanced alerts for people potentially crossing the road in front of you, too.

Laser Detectors

The police laser guns are very similar to the police firing a torch beam down the road except that it's not on the visible spectrum. This beam is quite narrow when it first comes out of the gun and may only be about a foot wide at 100 feet, but will spread to over a metre wide at 500 feet and keep on expanding out.

As the laser signal is only emitted when the police pull the trigger on the laser gun, if you are driving on a country road and come around the corner or over a hill to be greeted by a police laser speed trap, then a laser detector will probably only warn you at the same time the police are taking a speed reading - after all, their guns work at the speed of light.

If the police are on a dual carriageway or motorway and are firing at other cars in front of you, then you have a chance of detecting scatter from that beam when you are behind the target car and will get a bit of an advanced warning before the police get around to targeting you.

Although the police generally target the number plate when they take speed-readings, a sensor down by the number plate will really only alert you to the fact that you have already been hit, since its view is blocked by other cars on the road. For an advanced warning, a laser detector needs to be mounted on the dashboard or windscreen so it can see the road ahead like your own line of vision, detecting the laser as it passes through the windscreens of the other cars ahead.

A laser detector will work at whatever distance the police are trying to use their equipment at. For example if the police are setup on a very straight Roman road and are trying to catch people speeding a mile away, then the laser beam needs to be strong enough to travel a mile to your car, bounce off, and travel a mile back to the police guns to calculate your speed. The strength of the laser beam needed to complete the round journey means it's easily strong enough to be detected by a laser detector.

In practice, the police will not try and catch you speeding at such distances because as you can imagine, it's hard to pin point a laser beam at a vehicle a mile away that is travelling at speed, and furthermore they will not get a clear picture of the driver at this distance. It is actually harder to detect a laser at a closer range because the laser beam and scatter will be that much narrower.

GPS Detectors

Since GPS based detectors are working off a database they can alert you to the traditional fixed Gatso cameras as well as these digital Truvelo and SPECS cameras, although they cannot tell you if the camera is actually active or not. Being database-driven they can also be a bit more specific so you can set the precise warning range that you want, such as 500 or 1000 feet.

They can also be set to only alert you if the camera is on your side of the road and also tell you what the speed limit is at the camera location, since they can have this data saved in the database as well. Some of the most sophisticated units can even tell you the road the camera is on and vary the type of warning that the give you depending on whether you are actually travelling above or below the speed limit.