The environmental body An Taisce has expressed concern over reports that the National Roads Authority was made aware as far back as 2000 of "superior alternatives" for the M3 motorway route.
The controversial route through the historic Tara/Skryne area of Co Meath will result in the construction of a major by-pass of the existing N3 from Clonee to Kells, by-passing Dunshaughlin and Navan.
Archaeologists, historians and environmentalists have described the proposed route as an act of "cultural vandalism" which would destroy a vital part of Ireland's heritage.
Campaigners against the proposed M3 route say the valley is "one of the most culturally and archaeologically significant places in the world". Many of its monuments predate the pyramids of Egypt.
The Tara site is also now believed to be much more extensive than originally thought and those who are opposing the motorway claim the route would destroy innumerable surrounding artefacts and heritage sites deserving of State and international protection.
However, the NRA argues that the new route will be further from Tara than the existing N3. Business groups in Co Meath have also spoken out this week in favour of the motorway plan, claiming it will costs jobs in the county if it does not proceed.
The Irish Timesreported yesterday that plans to extend an archaeological protection zone around the Hill of Tara, in Co Meath, were abandoned after it became clear that the proposed M3 motorway would run through it.
An archaeological report compiled in August 2000, explicitly referred to "an expansion of the zone of archaeological protection afforded to Tara". However, despite the contents of the report, plans to extend the protection zone were later abandoned.
An Taisce said today that the NRA "was given clear direction" in one report that a route east of Skryne would be preferable in terms of archaeological impact, built heritage, flora and fauna, landscape and visual effects, air quality and noise.
"It has also emerged that this route was also recommended in a second, separate report also commissioned by the NRA in 2000. In an archaeological assessment, Dr Annaba Kilfeather of Margaret Gowen and Company, compiled in August 2000, stated that "the only unreservedly recommended route" would run east of Skryne because "it avoids the area of highest archaeological potential . . . and has the inestimable advantage of being largely invisible from the Hill of Tara".
Dr Mark Clinton of An Taisce's National Monuments and Antiquities Committee said that given increased public concern, there was now a "significant onus" on the NRA to clear suspicions and to make public whether it ever informed the Government of the contents of these reports.