'Specs' cameras monitor the average speed of car between two points
Average speed checks are on the way for Welsh drivers for the first time, BBC Wales can reveal.
New mobile cameras would monitor speed between two points, then issue penalty notices if the limit is exceeded.
BBC Wales Dragon's Eye has learnt the cameras are likely to be introduced on a stretch of the M4 motorway around Newport, where there is a 50mph limit.
The assembly government said the cameras were being considered and had been "used extensively" across the UK.
North Wales Chief Constable Richard Brunstrom said he wants the new cameras, which the assembly government is currently negotiating to buy, to be moved around Wales as much as possible.
Average speed checks on other stretches of motorway in Britain where there are 50mph limits has led to average vehicle speeds of 46mph.
Mr Brunstrom, the spokesperson on road policing for the Association of Chief Police Officers, added that he believed purchasing a 'Specs' average speed enforcement system for the M4 will give Wales the opportunity to adopt what he calls "a uniquely tailored approach to road safety across the country".
"You'll know that I think Wales has been rather tardy in introducing average speed devices," he told Dragon's Eye.
"They're commonplace in England and everywhere in Northern Ireland now and I'm very pleased the assembly has now indicated... (it will) go ahead with this because it is much needed.
"The equipment that's going to be ordered in Wales is mobile rather than fixed site - particularly so it can be moved around from one site to another where the need is greatest.
"I don't know quite how far that's going to go but I'm absolutely delighted that the first steps have now been taken with our total support."
The system works by monitoring a stretch of road with linked cameras that continually capture images of passing cars, regardless of which lane they are in.
The cameras note a car's number plate, and the average speed of the vehicle between two points, often miles apart, is then calculated.
If the driver's speed exceeds the limit, an offence is automatically recorded, along with images of the offending car, ready to issue a speeding ticket.
It is understood that the section to be targeted by the new cameras will be a stretch of the M4 around Newport where there is already a controversial 50mph speed limit in force.
There are ongoing works to widen the carriageways between junctions 29 and 30.
However, the restrictions extend beyond those junctions, which has led the Institute of Advanced Motorists to describe the limits as "nonsense".
The employers' organisation, the CBI, has raised concerns about the impact on business.
But assembly government officials have defended the speed restrictions, insisting they are needed "to improve safety and traffic flows for motorists on this section of motorway because of congestion on this stretch of road".
A spokesperson added: "We are considering whether average speed cameras - which are used extensively across other parts of the UK - could have a potential role to play in improving safety and traffic flows on a limited section of the M4."
It is now understood that after the road works are completed that a variable speed limit will be introduced on the stretch of motorway, probably in summer 2010, monitored by average speed checks.
The assembly's enterprise and learning committee is currently investigating road safety in Wales, but member Liberal Democrat AM Jenny Randerson said she had reservations about widespread use of average speed cameras.
"When you have that area that is very dangerous around Newport, then the average speed camera system is an extremely effective way of enforcing it - I think it is probably essential in that area," she told Dragon's Eye.
"But if they carry it on out to the area beyond then it will be difficult for people to keep to the limits and still drive in the normal way that people do on motorways."