Legal i

Speed detection and penalties

I was driving along a dual carriageway within the legal speed limit, at 60mph, and was signalled to stop by a policeman. He advised me that his speed detection device had recorded me travelling at 84mph, but it wasn’t me. I believe that the speed was captured from the car that was overtaking me – a white car also – and I believe that the policeman is mistaken. I told him of this, but he refused to listen. I already have three points on my licence, and because I am a new driver and have been driving for less than two years, if I accept the fixed penalty, it will take me to six points, which will mean an automatic ban. What are my chances of success if I should argue this in court? Incidentally, when I was in court for speeding the first time, I wasn’t offered a speed awareness course – can I take one for this latest offence, even though I believe it wasn’t me that was speeding?


A The effectiveness of speed detection devices and the ways in which they can give false readings varies according to the device used. It has to be a device approved by the Secretary of State, so if it is not an approved device, then its results cannot be given in evidence.


Hand-held radar guns, for example, work by a radar beam striking the moving vehicle and the frequency of the beam reflected back to the gun is changed in proportion to the speed of the vehicle. The gun measures the change and displays the speed of the vehicle on a screen for the operating constable. This reading can be saved in the machine. The guns have a range of 500 yards or more. There are at least five ways in which a gun can give a false reading: through low batteries; poor contact through car lighter sockets; radio or similar interference; reflection of the beam off a metal object (such as a lamp post) onto some other moving object; or measurement of the speed of another vehicle in the wide beam. A test on a smaller, nearer vehicle might pick up a reflection from a larger, more distant one behind. Usually, in such instances, the reading would not be steady and would jump from one vehicle to another.


If you plead not guilty to the offence, the police are obliged to serve on you details of the device used and will in any event serve you with statements about the evidence against you, including the device and how it was operated. The courts do not usually exercise much patience in the face of technical challenges to the technology employed, unless there is some other evidence that suggests there might have been a problem. If you had someone with you who could verify that you were not exceeding the speed limit, that would help a great deal.


You say the speed limit was 60mph, but that would only be the case if signs of the correct size, colour and placement indicated this. If the derestricted speed signs were displaying (a white circle with a diagonal black line through it), then this denotes the national speed limit, which is 60mph on a single carriageway, but 70mph on a dual carriageway, which is what you say you were driving on.


Offers of a speed awareness course are discretionary. You are very unlikely to be offered a speed awareness course, because the general criteria are:

You haven’t been convicted of any other speeding offences in the past three years;
You’ve been caught driving over 10 per cent plus 2mph of the limit, but below 10 per cent plus 9mph.

If you were in a 70mph zone, an offer could be made, as the criteria allow anything between 79mph and 86mph, but you have been convicted of a speeding offence within the last three years (you having said that you have been driving for less than two years), so you almost certainly will not be offered a speed awareness course.


You are correct in that if you accumulate six or more penalty points within two years of first passing a driving test, then your licence will be revoked and you would have to pass a new driving test before having your licence restored. It is therefore important that you take advice on the evidence that you are provided with, as to the device used to detect your speed and how it was operated, in case you have a technical defence that would result in your acquittal.


Designed by solicitors, tested by barristers and available around the clock, Road Traffic Representation is an online legal system that allows people accused of a motoring offence to get free advice on how the law will be applied in their case, and referral to a telephone helpline and representation by a barrister in court if required. Practising solicitor Martin Langan spent two years designing the system and creating the data repository which allows the software to analyse road traffic offences with the same authority as a solicitor.

Twitter: martinlangan

One Response

  1. Many years ago I got. Speeding conviction. I was riding a small motorbike on an icy road very carefully at about 15 mph. There was sheet ice and I couldn’t break or accelerate for fear of falling off. I went past a police radar vehicle, and was ‘ clocked at 42 mph’ . Since I had just come round a 90 degree bend on the icy road slithering and sliding it would have been lethal to be travelling at 42 mph.
    The policeman who pulled me up was very aggressive, and told me radar cannot be wrong. I have since found out that things like chain link fences along the road side can adjust the reading. On the same bit of road many months later there was a failed prosecution of a dumper truck driver at 52 mph??

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