The exhibition, showing all the routes which have been considered, marks the start of a public debate on whether the road needs to be improved and if so how it should be done.
A special 'planning conference' headed by an independent chairman will be held in November where all interested organisations and individuals can put forward their views and proposals.
Tony Duke, Highways Agency project director for the scheme said:
'We have identified several options to initiate debate and focus people's minds on possible options. The conference will give local residents, road users and organisations such as English Heritage and the National Trust the opportunity to present their views and to come forward with a viable route.'