Construction of a new £150m dual carriageway between Londonderry and Aughnacloy could begin late next year, the Infrastructure Department said.
The building work was due to begin several years ago but has been delayed by repeated legal challenges.
The most recent obstacle, a court ruling effectively meaning civil servants could not take major decisions in the absence of ministers, has now been overcome by legislation passed in Parliament which aims to unblock the logjam created by the collapse of Stormont power-sharing.
The Infrastructure Department said: “The A5 remains a very high priority for the department and it will now move immediately to carry out the necessary work to enable a fresh decision on the project to be taken during 2019.”
It confirmed construction work could begin in late 2019, subject to legal considerations and any further issues arising.
Parliament has passed the Northern Ireland (Executive Formation and Exercise of Functions) Act 2018, giving civil servants powers to take major decisions in the absence of ministers.
The roads project linking Counties Londonderry and Tyrone has been hit by delays due to court challenges.
The planned A5 upgrade involves a new 85km trunk road between Newbuildings and Aughnacloy and will cost about £150m.
A5 supporters say it will bring economic and safety improvements but opponents oppose the compulsory purchase of land and raise environmental concerns, calling for the existing road to be upgraded instead.
Sinn Fein West Tyrone MP Orfhlaith Begley said the A5 would improve connectivity in the north-west, and with Dublin, while SDLP MLA Daniel McCrossan said the delays had been “reprehensible”.
Construction Employers Federation managing director John Armstrong said the new legislation should be moved to unlock a slew of other construction projects.
He said it is now critical that all government departments follow the lead of the Department for Infrastructure by using the new legislation “to bring forward a range of capital works, both public and private sector, which are currently unable to progress for a variety of reasons”. In the continued absence of ministers, departments must use the act and associated guidance so that “greater certainty can be applied to all levels of public sector construction works”. he added.