Tam Diep Tunnel is a key component connecting the expressway network between Ninh Binh and Thanh Hoa provinces on the North – South transport corridor from Hanoi to southern Vietnam. The tunnel consists of two independent parallel tunnel bores separated by approximately 50 m.

The tunnel is part of Package XL10 under the North – South Expressway Project, Mai Son (Ninh Binh Province) – National Highway 45 (Thanh Hoa Province) section. The package was constructed by Son Hai Group, with the Thang Long Project Management Board under the Ministry of Transport serving as the project management authority. Vinh Hung was responsible for the supply of waterproofing materials and the installation of tunnel waterproofing systems.