The M42 trial is expected to be adopted on other motorways

The scheme will be adopted following a successful trial on the M42 motorway near Birmingham, Transport Secretary Ruth Kelly is expected to announce.

During busy periods, the hard shoulder was used as an extra lane and the speed limit reduced to 50mph. Emergency refuges were established every 500m.

A feasibility study found congestion and vehicle emissions were reduced.

The hard shoulder option is also cheaper than building new lanes to tackle congestion.

'Taken by surprise'

Sensors detect traffic build-up, which trigger signs telling drivers to slow down and use the extra lane.

If accidents happen, messages appear telling drivers the lane is closed, allowing emergency services to get through.

Rebecca Lush-Blum, from the Campaign for Better Transport, said: "The M42 trial that the government has been running for over a year now has shown that opening up the hard shoulder really does work, actually.

"And we were taken by surprise by the results.