Police Speed Cameras Part 2

[ukpuffy]

Thanks to Tim Baxter & Grunty who answered my previous question about this. But, I need to clarify, if I am on a B road going along doing 60 and a Police Car is on the other side of the road doing 60 coming towards me, can it's speed camera inside tell what speed I am doing as I am coming towards it?

[Tim Baxter]

"Speed camera inside"????

Speed cameras can't operate through glass.

If the speed detector is mounted externally then, yes, it can detect your oncoming speed.

Have you ever noticed that fixed speed cameras can be tripped by vehicles going to fast in the oppsite direction?

[Tim Baxter]

Should read, "too fast" and why shouldn't you do 60mph on a B road?

[twiglet4frog]

any road other than a residential road or specifically designated speed limit (marked by speed limit signs) are 60Mph except dual carriageway or motorway which are 70MPH.

To answer your question, Interior cameras on police cars measure police car speeds like a speedo and not other cars speeds, Police use them on video camera to be used as visual evidance to show how fast they were travelling in comparison to the car they were following (i.e doing 80MPH in a 30MPH and the car in front is maintaining its distance therefore has equal or greater speed to the police car)

The only other option they have is to use a device which they can press on the camera that when a car they are following passes a specific point (such as a speed detector marking..The Diamonds/Squares u often see on dual carriageways) they press it and when they hit the second set of markings they press again gives them an average time and distance thus allowing the camera system to give an average speed. Again this is following a car from behind.

The only other camera is an external camera to detect speed and these are nearl always located at the rear corner of the police car and pointing rearwards. It is unclear but thought unlikely these will work effectivly without the police vehicle stationary first.

[Grunty]

• My previous answer was a bit over-simplified.  As twiglet says., the speed of the oncoming car is not recorded by the onboard camera, which is often used to demonstrate the seriousness of the offence (danger to other road users etc.)  Vascar is the device that measures average speed betwen two points.  As you probably know, if you know two figures out of speed/time/distance you can calculate the other.  The device measures the time taken by the police vehicle to pass two points.  It knows the time, and it knows the speed from the police car's speedo.  It can now calculate the distance.  Now it is easy to calculate the other vehicle's speed between the same two points, which it displays to a decimal point.  Any of these readings can be left in the memory until needed.  Therefore the offending car can be travelling in any direction, or the police car can be stationary in a layby or on a bridge, provided the two points are in view and accuracy can be assured.