The main three detection types are: Police car speedometer, RADAR or Laser type devices or time/distance equipment (VASCAR etc). There are rules governing the way each of these is used and these rules must be abided by:

The Speedometer
The speedometers fitted to Traffic cars are not the same as those which manufacturers put into family cars. They are far more accurate, read in one or two mph units and are calibrated by an independent organisation and checked every day by the officers on duty (which is recorded) over a measured mile. In the event of an officer not recording the details of the calibration check it can be argued that the speedometer on the patrol car is not functioning correctly at the time of the alleged speeding offence. However the reading can be regarded as corroborative whether or not the speedometer has been tested, the weight to be given to the corroboration of an untested speedo is a matter for the courts to decide. A question about the recording of a calibration check should always be asked of the officer in any contested speeding case.

Sometimes a “beat officer”, meaning someone not given the training that the traffic officers go through, may stop you. Most forces don’t encourage this because not only are the speedometer in ‘Panda cars’ are never calibrated but there is the possibility that the beat officer will not be conversant with the correct procedures for speed checks. They may be able to liase with a traffic officer after the event to establish the correct procedure but this could very well mean that the information recorded is inaccurate – again, the whole accuracy of the check can be brought into doubt and the magistrates will be required to decide one way or another.

The proper method for checking a suspected speeder (by a calibrated speedo) is; the police car takes up position to the rear of the target vehicle then maintains that distance. The speed of the target vehicle is matched for 2/10th of a mile (generally) and no other vehicle must interfere with the check (by being between the cars for example). Traffic officers refer to this type of offence as “Failing to look in your read view mirror” meaning that you should clearly see a marked police car in good visibility.

NB: TRUVELLO
Inserted just after the paragraphs above on Speedo’s is this little snippet – policy normally states that you follow the target for a minimum of 2/10ths of a mile, but the TRUVELLO system measures over 1 metre only. TRUVELLO is a system where two cables are pinned to the road surface 1 metre apart and connected to a computer. The vehicle wheels trigger on and off – a bit like VASCAR but fixed. So it is possible to be prosecuted for speeding over much less than 2/10ths (like over a distance of 1 metre!). Connected to a box at the side of the road, the cables relay speed information to an officer who monitors it and radios to the ‘stopper’ further down the road. At the end of the check the cables are lifted by the officers and taken to the next check. They are only placed halfway across the road so other vehicles can’t give false readings, as you can see, it is a foolproof system but it has the “disadvantage” of being fairly visible to an observant driver, so it is not often used nowadays.

Radar
All Radar devices in the UK rely on the Doppler effect to detect speed, which is a proven physical property of any electromagnetic, or pressure wave, be it radio, light or sound. In the case of Radar, a signal is emitted from the device and some of it bounces back from an approaching vehicle. As the returning frequency is higher than when it was emitted, the speed is directly proportional to the change in frequency. This is very accurate.

The Radar device will always display the speed of the strongest returned signal. It is this fact that can be used against its accuracy in certain cases. If two cars of similar size are in close proximity, it will always display the speed of the closest vehicle. But, the signal strength not only depends on distance but size too – for example, a lorry behind you may emit a stronger signal than that returned from your car!

The signal can also be reflected from stationary objects such as road signs. This means that a signal could be picked up from a vehicle outside the wanted detection field. Officers do know this however and tend to pick sites with have a clear, unobstructed view of the road. They also take into account high-voltage power lines and other sources or interference.

All these points go to making certain rules for the operation of these handheld Radar devices:

• It must be operated by an officer on foot, not from a vehicle
• It must only be operated when ONE vehicle is isolated within the view
• If there is another vehicle in the field of view the check should be aborted
• The Radar device should not be aimed randomly – it is there to reinforce and corroborate the prior opinion of the officer as to the speed of a vehicle
• When the speed is indicated on the display of the Radar device it should be held on the vehicle for three seconds
• The distance that the Radar device must be used over is quite large – not only is the distance required for the assessment of the vehicle and its speed, but also the distance travelled in the three-second check and the stopping distance when signaled to stop. Using information on the back of the Highway Code, the calculated overall distance is just over 165 meters!

The Radar devices must be calibrated prior to every enforcement use. A police car (with a calibrated speedo) is driven towards the operator at a pre-determined speed and the two speeds are compared. The calibration check must be carried out by TWO officers and must be recorded. There are many occasions where two officers are not available and the check is not carried out. In the event of any of the above checks not being carried out, doubt could be cast on the manner in which your speed was recorded and that could be to your advantage.

It is frowned upon by forces when an officer “hides” in some bushes (for example), clocks your speed and secretly notes down passing cars’ number plates.

Time & Distance recorders
Visually Assisted Speed Computer And Recorder (VASCAR) is THE way that the police use to record your speed this way. Ever wondered what the white squares in the center of a lane were for? They are speed reference marks that allow VASCAR to be used. VASCAR can be used for ‘pre-determined distance’ or ‘following’ speed checks.

If a police car fitted with VASCAR is following you, when you pass over one of these reference points (reference points can also be STOP lines at a Pelican Crossing or a SLOW sign in the road) the time switch is turned on. When the police car passes over the same reference point the distance switch is turned on. Then they watch for you passing another reference point whereupon the time switch is turned off and the same with the distance switch when the police car passes that point. As both the time and distance is now known to the computer, the target vehicle’s speed is instantly displayed and is a very accurate figure.

The pre-determined distance check is even easier – both reference points need to be in clear view and all he does is operate the one switch. The reference points then need to be referred to in court.

VASCAR is most often used in following checks where you don’t even have to maintain an equal distance, you merely have to say you used the same fixed points on the road for both the target and yourself. Not widely known is this fact: It can be used for ‘opposing’ checks although it is not easy to do and is not commonly used. You trip the time switch for an opposing vehicle as it crosses a fixed point, you then turn off the time and turn on the distance as it passes you then turn off the distance when you pass the fixed point. Then you have the necessary for the time taken to travel a set distance and the computer does the rest. All that remains to be done then is turn and catch up to the offender!

Again, calibration is an issue – VASCAR has to be re-calibrated when new tyres are fitted or if the device has been removed for any reason, or at least weekly. A written record must be made in the vehicle log book and the officer’s pocket book.

The bottom line…
Another point worth remembering is that the speed device is used to corroborate the officer’s opinion of speed. HOWEVER two officers together can give an opinion of speed and successfully prosecute a speeding offence without a speed measuring device! It is merely necessary if it came to court and the Magistrate had to be convinced that the officer(s) are capable of giving an estimate – i.e.. years of driving, experience in the police etc. Of course all this only relates to offences committed in England. Scotland has different evidence rules.

In Kent (as an example), a log is kept of every speedo calibration done on each vehicle fitted with a calibrated speedo. The vehicle is tested once a week and also within 24hrs following a speeding offence. It is not done prior to every days patrol, this is fairly standard throughout the country and is lawful. Also, a vehicle fitted with a non-calibrated speedo can be used provided the speedo is tested within 24hrs after the offence and the speedo is found to be within the acceptable limits.

For all the devices mentioned above, with regard to calibration checks, certainly a log of the checks must be available to the court if requested but the motorist does not have the right to demand production at the roadside. Local procedure may allow the motorist to see the log but it is not enforceable in law. Don’t ask the officer questions about this at the roadside. If you were questioned about your ability to do your job how would you feel?

All this is policy remember. It varies from Force to Force. The only thing that is constant is the legislation governing the offence. How that legislation is enforced is down to the Chief of Police for that area.