LHASA, April 26 (Xinhua) -- 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. Gong Bin, project manager of Mila Mountain Tunnel of the...