The Department of Rail Transport has intensified oversight of the Den Chai–Chiang Rai–Chiang Khong railway project (70.6% complete), which includes Thailand's longest tunnel at 6.121 km. The Nong tunnel requires additional safety precautions due to poor rock quality; excavation work is progressing through four single-track tunnels. Track laying in the Nong tunnel is expected to begin in 2027, with the overall project targeting opening for freight and passenger services in 2028. DRT has mandated rigorous geological monitoring and engineering controls to manage structural risks.