The cameras work in all weather, do not use radar or flash, and never run out of film - unlike the "grey box" Gatso speed cameras in use in many British cities, of which only one in 10 contains film, reducing their deterrent effect.
The spacing between the new cameras - between 250 metres and 1,500 metres - means motorists who simply slow down on seeing a camera and then speed up when "out of range" will be caught. In early tests, 4,300 people were spotted speeding in a single day.
The first site is expected to be on roadworks on the M2 between junctions 4 and 6. Such stretches have high accident rates and injuries to workers because of contraflow systems and reduced lane widths.
But many motorists ignore mandatory speed reductions to 50mph - one Chief Constable was notably caught doing 80mph through roadworks.
The new system, called Speedcheck SVDD (Speed Violation Detection Deterrent) captures digital images of number plates and can deal with three vehicles per second. When the vehicle passes the second camera, a roadside computer calculates its average speed. If this is above a certain value, a notification is sent to the local police who can forward the details to the Driver and Vehicle Licensing Authority (DVLA).
The system uses infrared technology so that poor weather does not reduce its effectiveness. Radar detectors sold for car drivers will give no warning of the cameras' presence.
But the system could also be extended to catch road-tax cheats and stolen cars, because it is able to cross-refer with the Police National Computer (PNC) in three seconds. As it takes 36 seconds even for a car doing 100mph to travel a mile, that allows plenty of time to identify cars against national databases.
The Treasury is giving the DVLA pounds 400,000 for a pilot study to catch road- tax dodgers, starting in September, using similar technology to the SVDD system.
A spokeswoman at the Department of Transport confirmed that "the system can be selective in terms of tracing vehicles" and admitted that it raised "civil liberties questions". So far the system has only been approved for catching speeding cars.
The conventional Gatso radar-triggered roadside cameras were introduced in Britain in 1992. There are now an estimated 2,000 across the country, although many are left switched off because of the expense of keeping them permanently loaded with film.
Figures released in May showed that almost 400,000 motoring transgressions were caught on film in 1997, of which 86 per cent were speeding.Reuse content