The first batch of court summonses have just arrived by post at the homes of motorists caught speeding by the cameras. With the new system of fining according to means also in operation, some well-heeled drivers could be heading for very heavy fines without ever having felt the strong arm of the law on their shoulder - just an invisible beam emitted by a grey metal box on a pole.
If the large amounts of revenue generated by similar systems in Australia are anything to go by, the speed detectors are likely to be introduced in other parts of Britain. Supt Carman is thrilled with his new gatsometers, as they are known. 'We have five cars on the day shift, and if they're not having to deal with speeding offences they can be attending burglaries or trying to catch ram-raiders,' he says.
There is no doubt that the cameras - which are always accompanied by a host of signs warning of their existence - have put the frighteners on motorists. Supt Carman still takes to the highways on a BMW motorbike to oversee his manor, and has been amazed to find so much law-abiding motoring on the A40 and the M4.
One of his constables, PC David Kingston, agrees: 'In the first week they came in, it was hard to catch anyone for speeding.' But catch them the machines did - in that same week, one offender was snapped doing 109mph on the elevated section of the M4 into London.
For Supt Carman the 'gatsos' have arrived not a moment too soon. He is particularly concerned about the A316 as it crosses Twickenham Bridge. 'During the summer we put a camera on the bridge for three weeks and it recorded 22,931 cars doing 60-plus on a 40mph road. A third of them were doing more than 70. If things are that bad, we need one of these machines there. During the first week of them going live with the warning signs, we had 20 offenders - one of them was the same man twice. And look at this one here . . .'
Supt Carman shows me a crisp and detailed colour print of the rear end of a 3-Series BMW. The digital read-out shows the time the picture was taken - 6.23am - and the speed - 77mph. 'Seventy-seven miles an hour] That road has a dangerous bend with a queue of traffic often round the corner. You just don't need people like him, do you?'
Also in Supt Carman's rogues' gallery are photographs of a lorry that spilled several tons of tomato puree on the A1 - 'It doesn't wash off with water' - and a car whose driver jumped a set of traffic lights at 57mph, 30 seconds after they had turned to red - 'I don't know what he was up to. Mentally off and away somewhere else, I should imagine.'
The gatsometer was invented in the 1950s by a Dutchman, Maurice Gatsonides, who once won the Monte Carlo Rally. The units, which cost between pounds 15,000 and pounds 18,000, emit a radar beam which is reflected back by passing cars to enable calculation of their speed. If the speed is sufficiently fast, a flash light is triggered and pictures are taken at 1,000th of a second to freeze motion and allow the number plate to be identified. 'The light's very bright,' says Supt Carman. 'It's a bit like Saul on the road to Damascus. The driver must wonder what has happened.'
The gatsometers do not record every single motorist who exceeds the speed limit, otherwise the Superintendent and his officers would disappear under a sea of paperwork. 'We haven't set them marginally near the speed limit, so you've got a fair chunk of latitude,' he says. 'But if you're in, you're in. Don't ask me to say what they are set at, because I'm not telling you. But we're after the drivers who take two or three times as long as others to stop.'
It is thought that the trigger setting is probably around 20mph over the speed limit. Carman's patch has 21 sites, yet there are only four cameras in use. But even if there is no camera fitted, the box still flashes. There will therefore be an uncomfortable two-week wait before a summons either drops through the letterbox or does not.
In every new obstacle there is commercial opportunity and, sure enough, car magazines are currently filled with advertisements for in-car radar detectors costing anything from pounds 200 to pounds 400. Another aid is The London Speed Trap Map (The Clever Map Company Limited, pounds 3.99, available from bookshops). It shows the locations of speed traps and red-light cameras throughout the capital. Its intention is 'to encourage impatient drivers to drive more slowly . . . and lead to fewer road offences and legal penalties.'
Supt Carman is unimpressed by the electronic radar detectors, which resemble portable CD players and can be plugged into a car cigarette lighter. 'They're usually only telling you that you've just passed through a speed detector,' he explains. 'And by then it's a bit too late.'
For safety reasons the gatsometer directs its beams away from on-coming traffic, which is why it photographs the rear ends of cars. So, unless detectors can pick up bounced reflections from the backs of cars further along the road - or from an uneven road surface - it will usually be too late to slow down once the in- car warning goes off. (However, the technology can easily detect beams emitted from hand-held radar units, which have been used by British police forces for many years.)
But there is a more fundamental hitch. While it is not illegal to own a radar detector, using one is an offence under The Wireless and Telegraphy Act 1949. The Radio Communication Agency, which is attached to the Home Office, successfully prosecuted two radar detector sellers in June for incitement. All suppliers have now received a written warning from the RCA, which states that customers who are unwittingly prosecuted could sue them.
This makes suppliers reluctant to demonstrate or even talk about their wares. 'It's very unfair,' said a supplier from Surrey. 'Fifty per cent of motorists have them in the United States, where they are legal in the majority of states. All we are doing is encouraging people to be aware of their speed and not to break the law. I recently sold one to a magistrate.'
The gatsometer has disadvantages for the police as well. Because speeding cars are not stopped and drivers are not identified, impersonation of an offender is a possibility. 'I've heard of one case where a sales manager took the rap and the penalty points, because his rep was already at the limit of his points and any more would have got him banned,' said one dectector supplier. Such action is an offence, but might be hard for the authorities to detect or prove.
And what does Supt Carman think of a new kind of reflective number plate which, it is claimed, 'blinds' the camera and makes identification of the car impossible? 'Great,' he says. 'They work really well and give us an even better picture. We reverse the image and it comes out clearer. We've had three so far and they've all had summonses like everyone else.'
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