LTI 20.20 speed detection gun testing and approval information
Published 20 September 2013
© Crown copyright 2013
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FOI release 25645
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The LTI 20.20 TS/M laser speedmeter was approved for use in the UK in 1993 and passed the testing against the requirements of the Speedmeter Handbook 2nd Edition. We have enclosed the page of the test report which confirms this. (see PDF attached).
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The secondary check is only a check that the equipment was working at the time of the measurement. It is not the measured speed used for prosecution. The only speed measurement intended to be used for the prosecution is the primary speed measurement and prosecution on that basis should only proceed when the secondary check confirms the correct operation of the equipment.
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Section 5 of the Speedmeter Handbook contains the operational requirements of devices at all times – not just during approval testing.
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A series of short white lines are painted on the surface of roads covered by the fixed unmanned roadside cameras as a way of verifying the speed reading on the film. Because two photographs are taken of the speeding vehicle (0.5 seconds apart), it is possible to compare the two photographs and work out how far it has travelled in the interval using the check marks on the road. U sing a simple formula, the viewer can confirm the speed reading given by the camera. It must be stressed that secondary checkmarks are there to safeguard the motorist against a faulty or false camera reading. All automatic speed cameras are expected to conduct a second measurement of speed by some means different from that of their main operational principle, typically by two timed photographs showing distance travelled in that time by reference to road markings.
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Speed measurements were made at distances between 44.1 metres and 155.2 metres. We only have documentary evidence of testing the LTI 20.20 TS/M up to 155 metres. The conditions of its type approval do not restrict the distances at which it may be used. As long as there is an adequate return signal, the device’s functionality does not depend on the absolute distance of the vehicle from the device, and there is no necessity to test at every distance. Testing at one distance is sufficient to ensure correct operation at every distance within the range for which it is capable of registering the return signal. Beyond a certain distance the return signal will be insufficient to generate a speed reading.
6.Other hand-held laser speedmeters have been tested at ranges exceeding 155 metres. The following table indicates the type approved lasers for which we have evidence of a maximum tested range exceeding 155 metres (see attached PDF table for Approved Laser Speedemeters).