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Hi,

I just received a NIP for doing 38mph in a 30 zone (infringement date being 01/08/24). It's the first I've ever received in the UK over the several decades that I have lived here on and off.  I'm not looking to try to get off the penalty (though I wouldn't say no to that either) as I accept that I was over the limit, however I am interested to understand how the protocol for assessing speed via a mobile speed camera works.

I have been travelling through this village road close to where I live for the past 13 years and most of the motorbike-cop speed traps have been visible at the side of the road down one end or the other of the long, straight section of the road. At one end the road continues straight in to National Speed Limit (NSL)(60mph) on exit; there is a slight incline just before the sign. Usually I apply a bit of acceleration at this part which is only about 15m or so before the NSL sign. Recently a new speed-cop had been operating from in front or behind a hedge at this juncture (depending on your direction of travel) about 8m before the NSL where there is a small, village hall parking area. I had spotted him from the opposite direction on a few occasions (though I'm not travelling everyday through there), and couple of times in traffic going going out the village hall end. However, on this day I had been driving along the side of the road closest to where he would be operating and along hedgerows and did not see any sign of him or his tripod camera most of the way until I came level with the village hall where I had just applied some juice for the incline short of the NSL sign and suddenly he appeared just metres away tucked in to the carpark hedge a few meteres in, about 7m opposite the village hall. I immediately slapped the anchors on as I didn't know how much my speed may have been over on my gauge as I had only just applied the accelerator and the needle hadn't stabilised, but I saw it drop to 25mph, before passing him and hitting the NSL.

I haven't registered as the driver yet, as I will probably get a speed awareness course offer and my (recently acquired) car packed in just 2 days ago (with a concentric clutch slave cylinder giving up) and I had to get it towed home where I'll need to repair it myself over the coming week or so, and I don't know when I'll be mobile again to attend such a course so I'm holding off initially.

Anyway I was wondering about how the speed determination is made by the camera. Is it an instantaneous read or does there need to be a continuous read for a time period (like 2 secs) in order to determine speed and not record spurious variations such as change in the point of reflection on a car surface that may occur from movement of the car relative to the measuring beam that may cause the it to instantly jump in distance measured, such as from bonnet to bumper - or is this never really a practical issue, and would an instantaneous reading give a reliable indicator of speed? If anyone knows that can tell me how it works?

Thanks The Rookie, that does at least answer the technical side of the measurement. Do you know if there needs to be a minimum  distance of straight road in which to take these measurements? - I had heard some while back that something like 50m of straight line roadway was required in order to get a head-on reading, but this may have been for older equipment idk

I had heard some while back that something like 50m of straight line roadway was required in order to get a head-on reading, but this may have been for older equipment idk

even at 60mph it takes the measurement while the car travels a little over a cars length

I’m guessing that like many speed camera ‘facts’ it was heard in a pub? It’s never been true, older or newer equipment.

Most speed awareness courses were held on line during Covid and I believe that this has continued since, it was certainly the case when I did mine two years ago.

Quote from: Southpaw82 on August 09, 2024, 03:04:13 pm

If the reading is taken in 1/3rd of a second, why would there need to be 50m of straight road?

Where did you hear that?

Can't remember for sure, it would have been some time ago and this is based on other assumptions and not on the fact that the reading is done within 1/3 second and used as the only fact for speeding, ie the other assumptions perhaps being that an instant of over-speed may not be considered to 'define' speeding, such as an instance of over acceleration at gear change and that may be something like 2 secs may have been used so an accommodating straight stretch would be considered speeding - but this is just retrospective assessment of what it may have been before I found out it what I was told above

Those are certainly words…