An MLA has called for new powers extended to civil servants to be used to progress Northern Ireland's largest roads project.
A High Court judge yesterday confirmed that a decision to approve the A5 Western Transport Corridor scheme is to be quashed.
Mr Justice McCloskey made the order after the Stormont department who gave the go-ahead for the project announced it was no longer defending a legal challenge.
The outcome is based on the decision having been given in the absence of a minister.
The multi-million pound roads project linking counties Londonderry and Tyrone now faces further uncertainty and potential delay.
Opposition has come from the Alternative A5 Alliance (AA5A), a group of mostly farmers opposed to the proposed A5 route cutting through their land.
West Tyrone MLA Daniel McCrossan - a supporter of the A5 - said yesterday's ruling was no victory for the AA5A and called for Peter May, the permanent secretary at the Department for Infrastructure, to act.
He wants Mr May to use new powers extended to civil servants by Secretary of State Karen Bradley.
A bill introduced last month aims to give civil servants greater flexibility when it comes to making decisions.
Around 40 people have been killed on the A5 since 2006.
The scheme would involve a new 85-kilometre trunk road running from New Buildings, via Strabane, Newtownstewart, Omagh and Ballygawley, and terminating near the border at Aughnacloy.
Mr McCrossan said the AA5A group's actions have been "deplorable".
"The west and north west of this province deserve this road; a road that will prevent death, increase investment and grow connectivity." he said.
"Let me be clear, the absence of the DUP and Sinn Fein in government is what has put the A5 project at risk and certainly the reason the AA5A will get their way on this occasion.
"I am now calling on the department, its permanent secretary, to again move ahead with the legal orders necessary to progress the A5 and deliver first class infrastructure for the area. This must be soon as soon as practically possible."
AA5A spokesman John Dunbarr said his group did not know the department was going to withdraw from the challenge and believes the project is dead.
He said: "Our supporters and particularly the landowners who are in the firing line of this project are quietly breathing a sigh of relief and while nothing is very clear to us, our hope is that the department would shelve it altogether.
"The A6 is already being dualled and I don't think there is a need for two dual carriageways.
"The department only ever considered a dual carriageway but all other alternative means of solving a traffic problem - including reinstating a railway and our preferred option of fixing the existing road, widening it out and straightening it - the department didn't consider either of these."
A spokesman for the Department for Infrastructure said: "The A5 remains a very high priority for the department and officials and legal advisers are now considering how best to expedite the scheme."