Safe Speed Forums

"We do accept in certain atypical circumstances a device may be capable of producing inaccurate readings."

SPEEDING DEFENCES 3: Is incorrect use of a speed measuring device a valid defence against conviction for speeding?

speeding on A303
Barry Culshaw of our Motoring Offences team based at our Southampton office was consulted by P who had been summoned before Salisbury Magistrates Court in regard to an allegation brought by Wiltshire Constabulary of speeding on the A303 near Andover, Hampshire. The prosecution alleged that P was exceeding the 70 mph national speed limit for a dual carriageway by travelling at 104 mph. P was adamant that he was complying with the speed limit at the material time. The prosecution claimed that the police officer's prior opinion of excess speed was corroborated by a speed reading produced by an LTI 20:20 TSM speedscope laser speed measuring device. An expert's report was commissioned. Barry Culshaw, an experienced road traffic lawyer, represented P at trial where he was found not guilty, the court ruling that P was a credible and convincing witness, that there were breaches on the part of the police in complying with the relevant ACPO Code of Practice and the court could not be sure that it was P's vehicle that had produced the speed reading due to multiple vehicles in the vicinity of his vehicle at the time of the check and having regard to the beam spread of the laser beam at the distance at which P's vehicle had been targeted namely 676.5 metres.

Should better processes be in place since it needs to be formed 'prior' to the back up process ?

Clearly, it is hard to have a prior opinion and the maximum range of say an LTI 20-20. The other big problem is proving, in any real sense, that a prior opinion was ever formed. If the camera had a recording device built in that recorded a verbal comment by the operator of the prior opinion, I think that this would help.

LTI 20.20 TS/M SPEEDSCOPE OPERATIONS MANUAL 2008
...
CALIBRATION
Because a radio frequency is not used there is nothing in the instrument that can drift out of frequency. Therefore the tests mentioned above and the scope alignment test represent the majority of the calibration required. The speed calculations are referred to a crystal control time base which is guaranteed to have less than 100 parts per million (PPM) error over the full operating temperature of the instrument. Therefore additional calibration is not necessary but if verification of calibration is desired the following steps can be followed to verify proper calibration
of the range and timing accuracy of the instrument. These two functions are the two elements that calculate the speed measurement.
- 17 -
This can be done by following the procedures listed below:
a. Establish a known distance between two stationary points. For example this could be done with a metal tape measuring between a designated point on which the operator will stand and a sign or a telephone pole. The ranging accuracy of the Laser can be checked by having the operator stand on the designated point, aim the Laser at the target (whether it be a sign or telephone pole) pull the trigger and a "0" reading should be displayed for the speed measurement. By pressing the speed/range button the Laser should then display the correct distance.
The timing accuracy of the instrument is verified by the "0" speed measurement. An accurate "0" reading of a stationary target is identical in nature to an accurate 50mph reading of a moving vehicle. By verifying the ranging and timing accuracy of the instrument with the above test the two elements used to measure velocity have been checked and proper "calibration" is verified.
b. If additional verification is desired the instrument can be checked against a calibrated speedometer by shooting a stationary target from a moving vehicle and comparing the speedometer of the vehicle against the Laser. The stationary target is subject to the normal cosine error limitations and must be within a 10° angle off the road.
The LTI 20.20 TS/M Speedscope is not susceptible to radio frequencies and electromagnetic interference, therefore,

12, EVIDENCE
12.1
Presentation of Evidence
(a) The eventual success of any prosecution depends upon accurate observations by the officer operating the device and the professional presentation of evidence before the Court. It is in this area that the integrity of devices will be closely scrutinised.
(b) Operators should not only record evidence concerning the target vehicle, such as speed, direction of travel etc., but additionally, note the presence of any other vehicle in the vicinity, which may be used in defence when contradicting prosecution evidence.
Note: The need to document all evidence is obvious as the memory of the operator must dim with the passing of time.
(c) It must be remembered that the evidence of the equipment is only CORROBORATION of the operators prior opinion that the target vehicle was travelling in excess of the permitted speed limit for the road or class of vehicle.
(d) If the operator has any doubt as to the validity of the reading obtained by the device in comparison to his personal estimation of the speed of the target vehicle, then he will abort the check.
(e) Operators of devices should normally do so from positions where they will be clearly visible to the public.
(f) The target vehicle must be kept within direct sight of the operator of the device at all times throughout the period of observation and check.
(g) Positive identification of the target vehicle must be made by the device operator, to enable any enforcing officer to identify and process an offender.
(h) Whilst no legal requirement exists for the accused driver to be shown the speed recorded on the device, whenever this is possible he should be given that opportunity.
(Westwater -v- Milton, 1980).
(i) A trained police operator must necessarily be aware of the basic technical functions of the device. However, it is stressed that he is not technically qualified to give evidence on principles of the system nor the internal workings of the device. If such evidence is required, then an expert witness must be called.