Thailand's Denchai-Chiang Rai-Chiang Khong dual-track railway (323.1 km across 4 provinces) is 70% complete, with the ambitious Ngao Tunnel—Thailand's longest at 6.2 km—on track to break through in 2569 (2026). Three other tunnels have already been pierced; the project aims to open for passenger and freight service by 2571 (2027). Key challenges include geological variability and safety protocols for weak rock strata.