Inside out - Laser camera errors
From London News Online
By Unknown

September 19, 2005

Speed Gun - Inside Out investigates the reliability of mobile speed cameras, hidden on police motorcycles and cars.

Most motorists have a story to tell about getting a speeding fine. Every year across England and Wales over one and a half million people were convicted by speed cameras.

In the last year the numbers of mobile speed cameras hidden on police motorcycles, vans and cars have risen by more than a third meaning there are now over 3000 units in the country. These increases in mobile cameras will help raise over £20 million a year to the Chancellor. But how reliable are they?

Paul Cox got a speeding ticket whilst driving home. "I was driving a car with cruise control, set just under 70mph. I passed an unmarked police car that was doing checks. I was then pulled over and alleged to have been doing in excess of 90 mph".

Paul was convicted – but appealed and won. The court found there were discrepancies in the speed gun evidence used against him. "I was fortunate that as an ex-police officer, I was able to access information and to use my knowledge to know there was a discrepancy".
Paul Cox

There are several types of laser guns used in Britain; all work on the same principle. An operator targets the vehicle, fires the button and the machine sends out an infra red pulse which then works out the speed the vehicle was travelling at. It is however, crucial that the gun is held still whilst a reading is taken. If the operator moves the gun at the critical moment, some very strange readings are registered.

Dr Michael Clark, an expert in laser technology, demonstrates by pointing a laser speed meter at a stationary car. It registers a speed of 6mph. This is a process known as ‘slip effect’, caused by the laser beam accidentally moving sideways, in the split second it is fired. The gun is effectively tricked, interpreting the tiny movement of the beam as a speed.

In theory, if the gun moved along the side of a car during a reading, then this could add the length of the car to the distance travelled, adding up to 30mph to the speed recorded.

The manufacturer of the most commonly used gun in the UK, the LT1 20.20 says it is impossible to get a false reading on a moving vehicle. They are not alone in believing the guns can never be wrong, Inside Out discovered that the Home Office doesn't test speed guns for slip effect at all.

We decided we should see if the machine could be fooled. We used a truck fitted with the latest satellite technology, and 2 laser guns. On the 11th attempt we found a gun registering a slip problem, registering a much higher speed. This would put the driver at risk of loosing his licence. From a further 11 attempts, 6 wrong readings were recorded.
Police say their operators are trained to hold the guns steady. But the equipment is used without tripods at ranges of up to a kilometre.

Professor of engineering and author John Brignell explains it would be very difficult to keep the device steady. "If you get a pair of powerful binoculars, and try and focus on the number of a moving car 500 metres away – it’s quite difficult"

He says that an operator, pointing at a car 500 metres away, would only need a minute movement to slip off his target. "Very roughly, it’s the camera moving about the thickness of a human hair". Teletraffic, the police and the Home Office declined to take part in our programme, so we were unable to get hold of a gun here. Our tests used one from the US. In a statement, The Association of Chief Police Officers said our experiment was "misleading" because the UK-approved device uses different "error-trapping software" to the American version.

They also said "The Home Office Scientific Development Branch is of the opinion that the UK version will perform within permitted tolerances if used in accordance with the current published ACPO enforcement guidelines and will not replicate the errors shown by the American device".

Yet a report, obtained by Inside Out and written by Frank Garratt, Managing Director of Teletraffic suggests both versions of the LTi 20-20 are the same because the gun used by British Police is identical to the version used by NASA. And NASA then told Inside Out that the version they use is the American version. All of which seems to suggest that the UK and American speed guns are identical.

Dr Clarke believes the UK version is susceptible to error. "We used a US device for our tests; I can see no reason why the UK device should not suffer the same problems, both are based on the same technology and principles, with some minor variations".

Dr Clarke would welcome the opportunity to properly test an UK approved device so as to clear up any doubt about the reliability of the speed measurements made by this device.

The Home Office has declined all requests to do such testing. So, who is right? The Home Office or Dr Clark?

Statement

After transmission Meredydd Hughes of the Association of Chief Police Officers of England, Wales and Northern Ireland (ACPO) gave this statement:

"I believe this programme will mislead the public by implying that speed detection devices used and approved in the UK may be inaccurate without the evidence necessary to back this up.

"The programme focuses on a LTI laser speedmeter designed for the American market, which is not a Home Office type approved device. The American version of the LTI laser speedmeter uses a different version of software to that approved for use in the UK. In particular, the Uk version has different error trapping software contained with it and it has been subjected to Home Office type approval testing, recognised as the most stringent in the world, to ensure its accuracy.

"The Home Office Scientific Development Branch is of the opinion that the UK version will perform within permitted tolerances if used in accordance with the current published ACPO enforcement guidelines and will not replicate the errors shown by the American.

"Offenders should be aware that if they decide to plead not guilty based on viewing this programme but are subsequently convicted, they are likely to get additional penalties imposed upon them by Courts in excess of the conditional penalty they would have received."

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