We have received a request under the Freedom of Information Act 2000 for the following:
“I am in receipt of a notice of intended prosecution for speeding - allegedly 46 mph in a 40 mph zone, recorded by a RedSpeed camera.
I do not believe that I was over the limit, so I requested photographs to carry out a secondary check, to reassure myself that there was no mistake.
However, initially the operators of this camera refused to tell me the interval between the two pictures or offer any sort of explanation.
I was impressed by your desire to be open and transparent when a search took me to your site, so I would like to ask what I need to look for in the pictures, which I think are extremely poor, or how the RedSpeed camera sets the interval between flashes/pictures.
I have received some information from Avon & Somerset safety camera partnership (which I reproduce below) but I find it slight baffling!
The interval between flashes on RedSpeed cameras vary, as the photographs are not taken at a set time interval but at a set distance apart, therefore the time interval between photographs will depend on the speed of the vehicle. The 2nd photograph is taken at a set distance of 10 metres from the 1st photograph (the camera is triggered by a series of sensors embedded into the road surface) and the time interval between each photograph is read in milliseconds. The viewers will carry out a visual check to ensure that the vehicle has travelled between 9 and 11 secondary check marks (the white lines on the road which appear at all fixed speed camera sites) which allows for slowing down or speeding up - these marks are spaced 1 metre apart. Additionally, as part of the Type Approval, there is a software programme on the RedSpeed terminal that performs a secondary check
How does the camera know that you have travelled 10 metres?
If this is calculated from the speed at which you passed over the sensors, then how is accuracy maintained ~ for instance if the “clock speed “ which monitors the sensors was to become faulty, then the flashes would also be faulty and the error not be detected from the photographs?
At least with a GATSO, as I understand it two types of measurement are in place - radar AND timed secondary check. Any discrepancy would show in a series of differing readings.