We have a received a request under the Freedom of Information Act 2000 for the following:
“Is it mandatory for a secondary check to be carried out at all unattended automatic devices?
I have been able to ascertain from independent sources that the Truvelo Combi S Speed camera works with Piezo electric sub-surface sensors installed in the road. Is it correct to assume that two sets of measurements are taken between the first two sensors 1 and 3 and the second two sensors 2 and 4?
Does the camera system determine the time taken for the front axle of a vehicle to travel from sensor 1 to sensor 3 and sensors 2 and 4, which provides a second measurement? Are these the results processed separately to produce two totally independent speed measurements accurate to 0.1 mph, as advised in your response? If the speed measurements are greater than 2 mph will a zero reading result? Is it correct to assume that the lower speed recorded is rounded down and used to determine when a violation has occurred?
The secondary check, from what I understand, is the presence of three white lines marked on the road, the middle of which is 1.8 metres from the last sensor. The other two lines are 18 cm before and after the middle line, which allows for the 10% margin of error which you refer to in your response. This distance is an exact measurement and if the Piezo electric sub-surface sensors detect a speeding violation has occurred the camera will be triggered to take a photograph at the projected time when the vehicle’s front wheels are on the secondary, three white check lines. Is it correct that the Piezo electric sub-surface system works by vehicle axle detection and that the secondary check photograph should only be taken when the vehicle’s front axle is immediately above the middle white line. Is my understanding of the secondary check correct?
The “ACPO Code of Practice for Operational Use of Road Policing Enforcement Technology” states at paragraph 13 - Sensor Operated Roadside Speedmeters - that “Operators must be aware of the potential for certain axle configurations to create artificial readings. Compliance with proper operating procedure will ensure no inappropriate prosecutions being mounted.” In view of this warning by ACPO to operators of such enforcement equipment is it not incumbent upon the Statutory Agencies to make detailed information available to the general public about how Piezo electric sub-surface sensors operate and why, when and where these sensors should trigger a speed camera, such as the Truvelo Combi S Speed camera, to take a photograph of an alleged speeding violation?”
We released the following information on 11 June 2007.