THE proposed A5 road scheme between Derry and Ballygawley is estimated to cost £870 million to construct, the infrastructure minister has said.
Sinn Féin's Chris Hazzard said the figure does not include scheme development costs ahead of construction, which is due to begin in late 2017.
He said the full cost would be "significantly influenced by the timing of delivery of the various phases of the scheme".
The current estimate for the phase from New Buildings to north of Strabane is £150m based on a construction period of 2017-19.
The section from south of Omagh to Ballygawley is estimated to cost £225m based on a similar timeframe.
And the estimate for the north of Strabane to south of Omagh phase, due to be built between 2021 and 2023, is a further £495m.
Details were given by the minister in response to an assembly question from the SDLP's Daniel McCrossan.
The West Tyrone MLA said: "I want to see the project fully delivered as the people of the west deserve better than the position we are in now.
"The minister must ensure that there are no further delays or mishaps to ensure that the costs do not continue to escalate."
Earlier this month a campaign group opposed to the A5 scheme launched a second legal challenge to the project.
In 2013, the Alternative A5 Alliance won their previous judicial review after the court ruled an environment impact assessment had not been carried out properly.
The Department for Infrastructure plans to oppose the latest legal challenge.
