Greenwell freight tunnel breaks through after 19 months of boring

The 8.4 km Greenwell freight rail tunnel beneath the Eastlinden Hills broke through on April 14, 2026, completing the longest single bored segment in Welsh railway history.

Breakthrough

The tunnel-boring machine 'Mererid II', operated by Costain Eildon Joint Venture, completed final breakthrough on the 8.4 km Greenwell freight tunnel at 04:18 BST on April 14, 2026, beneath the Eastlinden Hills in mid-Wales. The 19-month boring phase was completed approximately seven weeks ahead of schedule. The tunnel will eventually carry single-track freight rail between an intermodal terminal at Llanfeirion and the existing Caerleon Junction.

Engineering

Mererid II is a 9.7-meter-diameter earth-pressure-balance machine with a 4,200 kW cutterhead. Maximum advance rate during the project was 28 meters per 24-hour day, achieved during a three-week stretch in October 2025 through soft-claystone country. Project engineers reported minor methane intrusion in two boring sections that required forced ventilation upgrades but did not stop the bore.

Funding

Total project budget is £612 million, of which £478 million is Welsh Government bond funding and £134 million is a contribution from Network Rail Cymru. The project is expected to remove approximately 38,000 truck journeys per year from the A470 corridor once freight services begin operating in late 2027. There is no provision in the current contract for passenger rail use of the tunnel.

Next steps

Following breakthrough, the next 14 months are dedicated to internal lining, drainage installation, signalling, electrification at 25 kV AC, and emergency-access cross-passage finishing. Service commissioning begins in summer 2027 with a six-month signed-test phase before regular freight service. Welsh Transport Minister Cerys Hopcyn-Yates called the breakthrough 'a milestone for modal-shift logistics in Wales' in a statement issued from the Llanfeirion portal.

Key facts

The 8.4 km Greenwell freight tunnel broke through on April 14, 2026.
The tunnel runs beneath the Eastlinden Hills in mid-Wales between Llanfeirion and Caerleon Junction.
The boring phase was completed seven weeks ahead of schedule.
The TBM Mererid II is 9.7 meters in diameter with a 4,200 kW cutterhead.
Total project budget is £612 million.
The contractor is Costain Eildon Joint Venture.
Maximum advance rate was 28 meters per 24-hour day during October 2025.
Welsh Government bonds funded £478 million; Network Rail Cymru contributed £134 million.
There is no provision in the current contract for passenger rail use of the tunnel.

Details