The Prime Minister is being urged to step in to decide on the future of traffic around Stonehenge.
Other projects cannot progress until the road scheme is approved
The RAC has written to Tony Blair, asking him to get personally involved after a series of u-turns and delay.
The motoring foundation favours putting the A303 through a 1.3-mile tunnel, bored into the Wiltshire countryside.
The scheme was recommended after a public inquiry, but was put on hold by the Department for Transport when its costs rose to £510m.
In his letter to Mr Blair, RAC Foundation chairman David Holmes said: "Only you have the authority to cut through departmental inertia and get some action."
A long-awaited visitor centre and rail link for the ancient site cannot go ahead until the government has sanctioned the road improvements.
Mr Holmes added: "Because the cost estimate for the scheme rose to £510m, the Department for Transport insisted on re-examining some of the options which the public inquiry ruled out.
"This is a backwards step, as any of these alternatives would have to be the subject of further consultation and full public inquiries. None could start for a decade or more."
Paul Holmes MP, Liberal Democrat Spokesperson for Arts and Heritage said: "I believe that only the published scheme of a 2.1km short-bored tunnel offers a practical solution without causing further damage to the archaeological remains.
"This scheme will prevent traffic damaging the stones and will allow visitors to see the monument without the blight of a major road running across the site.
"It is time for the government to make its mind up and back the scheme."