THE technology to be used to charge drivers in the Manchester congestion zone was rejected as impractical after a trial.

But transport bosses in Manchester will use the `tag and beacon' system as they say it is the most cost effective.

With tag and beacon, a tag carrying a unique ID is placed inside the car and small receivers are positioned around the charging zone.

As the tag passes the beacon, they communicate using radio, microwave or infra-red transmissions.

Though widely used on motorways a report by Transport for London in 2005 concluded it would not work well in an urban environment.

But a GMPTA, spokesperson said: "Tag and beacon is the most cost effective technological solution available to date."

The system works on motorways because gantries are mounted above lanes, but in built-up areas they would be mounted at the roadside.