(ECNS) -- Construction on the last pivotal tunnel on the Lhasa-Nyingchi section of the Sichuan-Tibet railway was completed Tuesday.
Milin Tunnel was considered the "hardest nut to crack" among railway engineers.
It is 11.56km long with an average elevation of 3,100 meters above sea level.
Milin Tunnel is the 47th and last tunnel completed along the section.
The entire Lhasa-Nyingchi section is 435km long, 75 percent of which are bridges and tunnels.
It is expected to be completed in 2021.