The Minister for the Environment, Mr Roche, has said he will make a decision "as soon as possible" on whether to require the M3 motorway to be rerouted away from the Tara/Skryne valley after receiving an expert archaeological report on the 38 sites along the proposed road.
The Minister has received a similar expert report on the Woodstown Viking site along the planned Waterford bypass.
This report indicates that the Viking site is far bigger than originally identified, stretching a further 120 metres along the proposed route.
Under new legislation, the Minister has responsibility for issuing orders for how the archaeological sites should be treated.
He can decide that the roads could be allowed through the sites, which would be preserved "by record", similar to the situation at Carrickmines.
Alternatively, he can order that the site be fully preserved, meaning that the new roadways would have to be rerouted.
Mr Roche told The Irish Times yesterday he would consider both reports together, and was "very conscious" of the time pressures regarding both projects.
Both reports will be examined by archaeological experts in his Department, and they will be advising the Minister.
Both the M3 and Woodstown sites have been the focus of campaigns by locals and academics to have the roads rerouted to preserve the sites.
Last week a petition from the Save Tara Skryne Valley group, signed by 10,000 people, urged the Minister not to allow the excavation of the sites on the M3 to go ahead.
It claimed the proposed route "unnecessarily traverses and partially demolishes the national monument of the Hill of Tara".
The letter also warned that a decision to proceed would be contrary to Irish and European law because it would enable "Ireland's premier national monument to be excavated and dissected by a motorway project when there were alternative routes considered that did not encroach on the monument".
It was accompanied by letters of protest from British archaeologists, the Archaeological Institute of America and Irish and international academics.
The Waterford report, which identified an additional area of "archaeological potential" in marshy land adjacent to the original site discovered, has raised serious problems. Even if the Minister decides to allow the excavation to go ahead, the costs and delays involved could be significant.
The original Woodstown site - believed to have been a large Viking town - has already been described by archaeologists as one of the most significant Viking sites in Europe. The National Roads Authority is drawing up contingency plans should the road have to be rerouted.
Yesterday Mr Roche said the new area uncovered was "clearly going to have a material impact" on his decision.
Under the National Monuments legislation, a rerouting of either road would not necessarily delay the project as only the rerouted section would have to go through a new planning process.