Motorists could be asked to drive on the hard shoulder of Sussex motorways within two years in a desperate bid to tackle congestion.

A stretch of the M23 has been highlighted as a location that could benefit from the radical measure which the Government says is a cheaper alternative to road widening.

Ministers also vowed to consider marking out dedicated lanes for car-sharing or charging to keep traffic moving on the motorway.

A feasibility study into extending a trial of hard shoulder running on the M42 near Birmingham identified about 500 miles of England's motorways which could benefit from using the hard shoulder as an extra lane.

It includes the M23 between junction ten, the major intersection between the A264 and A2011 to the east of Crawley, through Junction nine at Gatwick, to junction eight, where the motorway meets the M25.

A spokeswoman for the Department for Transport, which published the study, said: "These areas would benefit most from congestion relief and are the priorities for taking the process forward."

The study found there was a "strong economic case" for implementing hard shoulder running schemes more widely across the motorway network and concluded that, in the medium term at least, most of the benefits of planned motorway widening could be achieved through hard shoulder running "at significantly lower cost".

Even where widening was not previously planned, the use of the hard shoulder - with a 60 mph speed limit - was found to offer "good value investments".

Further work will be undertaken on the designs, costs and benefits at particular locations and stretches of motorway and firmer plans published by the end of the year.

Launching a new study into the proposals, which could take between two and five years to implement, transport minister Rosie Winterton said the scheme would "tackle congestion in our towns, cities and on the motorways in a creative way which will be a win-win for the motorist".

She added: "Experience shows that new road capacity has to be properly managed if it is not to simply fill up.

"There is a compelling argument for car-share or charged lanes, which have been used for some time in the US.

"In order to get maximum benefit, access to car-share lanes is limited to vehicles carrying passengers, or single drivers willing to pay a toll. I intend to explore the possibility for taking a similar approach here where we are adding new capacity."

RAC spokesman Adrian Tink said: "We are broadly supportive of further hard shoulder running due to the success of the M42 trial but the same level of investment has to be made with other schemes to protect the safety of motorists.

"We've come to recognise that building ourselves out of motorway congestion is not a viable alternative, and so the extension of hard shoulder usage does offer an alternative. But extending it on the cheap will jeopardise driver safety."