Aerial photo taken on April 26, 2019 shows the Mila Mountain Tunnel, a part of the high-grade highway linking Lhasa with Nyingchi in southwest China's Tibet Autonomous Region. The world's highest highway tunnel was open to traffic on Friday at an altitude of over 4,750 meters above sea level in southwest China's Tibet Autonomous Region. The two-way tunnel is over 5.7 km long, which is a part of the 400-km highway linking the regional capital of Lhasa with Nyingchi in the southeast of Tibet. Construction of the tunnel started in 2015 on the 5,018-meter-high Mila Mountain, and it was completed on Monday, helping shorten the 18-km distance over the mountain to 5.7 km. (Xinhua/Li Xin)