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The Court of Appeal’s decision on the A5 Western Transport Corridor marks a significant turning point in one of Northern Ireland's most high-profile and long-running infrastructure projects.
On 6 October 2026, the Lady Chief Justice Dame Siobhan Keegan delivered a summary of the Court of Appeal’s judgment, overturning the 2025 High Court judgment, which had prevented the Department for Infrastructure (DfI) from proceeding with the first phase of the A5 scheme.
The judgment will be welcomed by government, businesses, transport stakeholders and campaign groups who have long advocated for the project on road safety and economic development grounds. It also provides important guidance on how courts will approach challenges to major infrastructure projects where climate change obligations are engaged.
Background
The A5 Western Transport Corridor is a proposed major upgrade of the existing A5 route between Derry and Aughnacloy. The project, estimated to cost approximately £1.7 billion, would deliver a new dual carriageway along a key north-south transport corridor linking the north-west with Belfast, Dublin and the wider island economy.
The scheme has been contemplated for almost two decades and has faced a series of delays, including multiple legal challenges.
In 2024, DfI approved progression of the scheme. However, that decision was challenged by the Alternative A5 Alliance, a group representing landowners and residents concerned about the project's environmental and agricultural impacts.
The High Court decision
In June 2025, the High Court found in favour of the challengers and quashed DfI's decision to proceed. The Court concluded that the Department had not adequately demonstrated compliance with obligations arising under the Climate Change Act (Northern Ireland) 2022, particularly in relation to emissions reduction targets and Northern Ireland's wider net-zero commitments.
The High Court also identified concerns regarding aspects of the environmental assessment process and the Department's consideration of certain human rights issues. As a result, the project could not lawfully proceed on the basis of the impugned decision.
The ruling was viewed by many as potentially significant beyond the A5 itself, raising questions about how major infrastructure projects would be assessed against increasingly stringent climate change obligations.
The Court of Appeal's decision
The Court of Appeal has now reversed that position.
It held that the High Court had erred in its approach to the statutory climate obligations and wider policy context, and that although the A5 scheme would increase emissions, that fact did not of itself prevent the project from being authorised.
The Court also allowed the appeal on the EIA and human rights grounds.
The key issue: section 52
At the centre of the appeal was section 52(1) of the Climate Change (Northern Ireland) Act 2022, which requires Northern Ireland Departments to exercise their functions, so far as possible, in a manner consistent with statutory emissions reduction targets and carbon budgets.
The Court held that section 52 imposes a real and mandatory obligation on departments, but that the obligation is one of rational and informed decision-making rather than an absolute prohibition on projects that generate emissions.
The Court made clear that the existence of statutory emissions reduction targets does not preclude approval of projects which may increase emissions, provided the relevant decision-maker has properly assessed the project's impacts and reached a rational conclusion that its decision is, so far as possible, consistent with the statutory framework.
Why this decision matters:
1. A more nuanced approach to climate challenges
The judgment is likely to be viewed as an important statement on the interaction between climate change legislation and infrastructure development.
The Court appears to have rejected an approach whereby any increase in emissions automatically renders a project unlawful. Instead, decision-makers retain a degree of discretion to balance climate considerations against other legitimate public interests, such as, in the present case, road safety, connectivity and economic growth, provided their decision is rational, evidence-based, and aligns with climate obligations.
For promoters of major infrastructure projects, this will provide reassurance that compliance with climate legislation will be assessed in a practical and contextual manner.
2. Implications for future judicial review
The decision is also likely to be closely studied by public authorities and developers involved in large-scale projects across Northern Ireland.
While climate considerations remain a critical part of decision-making, the judgment suggests that courts will focus on whether those considerations have been properly assessed and integrated into the decision-making process, rather than requiring proof that an individual project will have no adverse emissions impact. Future challenges may focus less on whether a project increases emissions and more on whether the decision-maker gathered sufficient information, considered the relevant climate evidence and lawfully reached its conclusion.
The extent of these implications will become clearer upon the publication of the Court of Appeal’s written judgment.
3. Momentum for the A5 project
From a practical perspective, the judgment removes a major legal barrier to delivery of what has been described as the largest road infrastructure project ever undertaken in Northern Ireland. The focus now shifts to delivery of the project.
4. Certainty for the construction industry
The biggest significance for the construction industry is certainty.
DfI had effectively been treating the A5 litigation as a test case for major infrastructure approvals. The Department explicitly said that moving ahead with other major schemes could create uncertainty and increase the risk of further legal challenges.
With the Court of Appeal rejecting that legal interpretation, departments have considerably more room to resume procurement and move projects towards contract award and construction.
For contractors and consultants, that potentially means more large projects moving to procurement stage, particularly on large transport schemes that had been held at approval stages.
How ALG can help
The judgment underlines the growing importance of ensuring that climate considerations are integrated into decision-making from the outset of a project.
Our planning and environmental, public law, construction, procurement, and real estate teams are well placed to provide joined-up, expert advice to public authorities, statutory bodies, developers and infrastructure promoters on the full lifecycle of public and private infrastructure projects, from land acquisition and land rights, planning strategy, environmental compliance and regulatory issues, through to judicial review, procurement processes, and construction delivery.
As climate-related challenges continue to develop, ensuring that decisions are supported by a robust evidential record and a clear assessment of statutory obligations will remain essential.
For more information, please contact: Micaela Diver, James Flanagan, James Pringle, Stephen Geoghan, Cara Hughes and Paul Nugent.
Date published: 8 October 2026
