The High Court in Belfast will later decide on the future of the A5 road.
Since the project was first proposed in 2007, 57 people have died along the road, linking Donegal and Monaghan through Tyrone and Derry.
Stormont ministers gave the £1.2 billion project, which is set to receive €600m in backing from the Irish Government, the green light in October last year.
The upgrade would see it turned from a single carriageway with some passing lanes to a full dual carriageway along an 85km stretch from Derry to Aughnacloy in Co. Tyrone.
Preparation work had already started on parts of the scheme, and in March this year, the Infrastructure Minister visited a location where some advance works were underway.
However, landowners along the route have been fighting the case and began judicial review proceedings against the dual carriageway.
The case was heard over several days earlier this year, and the judgment will be delivered today.
The umbrella group, known as the Alternative A5 Alliance, contended it would breach legislative targets set out in the Climate Change (Northern Ireland) Act 2022 to achieve net-zero greenhouse gas emissions by 2050.
Lawyers acting for those in favour of the road claimed objectors were presenting “private interests disguised in the cloak of environmentalism”.
