Speed camera triggered at 31 in 30 zone

[ACE997]

I was doing 31 in a 30 zone and to my surprise a speed camera flash was triggered by my car. Has this happened to anyone else or can anyone offer an explanation why the camera was triggered?

I thought that my speedo would slightly overstate my speed
I was definitely doing a constant 31mph according to my head up display
There were no other cars near me to trigger the camera
It is definitely a 30 zone

Could the camera have misread my speed or is 31 enough to trigger the camera? I thought the trigger was at least 35.

[ACE997]

Thanks for the replies guys.

creampuff said:

Was it a Gatso (large) or digital (small) camera? Did it flash only once?

If it was a Gatso and it flashed once, don't worry about it.

Large Gatso. There was a double flash.

munroman said:

Could it have been a vehicle going the other way, there is a camera near Parkhead in Glasgow which is always being set off by vehicles speeding on the opposite side of the dual carriageway.....

No cars were going the other way. This was the second thing I checked (my speed being the first). When going the other way, I have noticed that it triggers only above 35mph. Which makes this case even more mysterious.

charltjr said:

Are you running on the factory spec wheels and tyres? Your speedo might be out if not.

Yes, factory spec. I have thought about this too, the car is only a couple of months old and so the tyre wear is low and tyre circumference is near its largest. I even considered tyre pressure but the onboard tyre pressure monitor says all tyres are normal. I have also checked the calibration of the head up display vs the speedo and they match. I have passed this camera many times at an indicated 29 or 30 mph and it did not trigger. This was the first time I pushed it to 31mph.

Edited by ACE997 on Sunday 6th April 10:37

[ACE997]

Snowboy said:

The OP mentions his speedo over reading and his HUD showing 31.

Is the HUD in this case actually the speedo or is the HUD a separate GPS speedo.
Was the car speedo showing 38 and the GPS showing 31?

That would change the story somewhat.

HUD showed 31mph. I have subsequently compared HUD vs speedo and they seem in line. I still need to get a separate GPS into the car to compare average GPS speed vs HUD/speedo.

[ACE997]

Snowboy said:

What do you mean by HUD?
Is it an aftermarket add on or something built into the car?

It's very unlikely a camera would be set to trigger at 31mph.
That leaves 2 reasonable options.

1. The camera was faulty in some way.
2. You were going faster than you thought.

Wait and see if you get a ticket I guess.

HUD = BMW's factory fitted head up display

1. Possible
2. Indicated speed was 31mph on the HUD just before the double flash

[ACE997]

GPSHead said:

I believe that when a Gatso is out of film, some SCPs will set it to trigger at much lower speeds (potentially anything whatsoever above the speed limit) than when it contains film, and it will still flash twice. I think the "rationale" is to basically scare anyone who is at all over the limit (which might actually make sense if that was a significant safety factor, etc, etc).

I predict that you won't hear anything more.

In case anyone searches this thread in future and wonders what the outcome was... 6 weeks have now passed and I haven't heard anything more. I think that the above explanation from GPSHead seems the most likely explanation.