Vehicles may be allowed to use the hard shoulder

Ministers had previously said the best solution to congestion was to widen the road between junction 11a at Cannock and junction 19 at Knutsford.

But the agency now says it is looking at alternatives on some sections.

BBC Midlands transport correspondent Peter Plisner said this may include letting vehicles use the hard shoulder, as has been trialled on the M42.

Other attempts to ease congestion on the M42 have included restricting the speed of vehicles.

'Different 'solutions''

The government announced in July 2006 that plans to extend the M6 toll road north of junction 11a would be scrapped but that efforts to widen the motorway would continue.

But the Highways Agency's website now reads that "the current M6 study work is considering in outline the cost, environmental impact and economic value of widening".

It adds: "It should be recognised that different lengths of the M6 may lend themselves to different "solutions" to take account of differing circumstances and pressures."

A spokesperson for the Highways Agency said no decisions had yet been made.