Hai Van Tunnel 2 in central Vietnam has opened to traffic Monday after four years of construction.
Connecting Thua Thien-Hue Province with central hub Da Nang, the tunnel of 6.2 kilometers (3.85 miles) is the longest road tunnel in Southeast Asia and helps reduce traffic pressure on Hai Van Road Tunnel 1.
The new seven-meter-wide two-lane tunnel runs alongside Tunnel 1 on National Highway 1A as part of Hai Van Pass, which rises 500 meters above sea level as the natural border between Thua Thien-Hue and Da Nang.
Invested by Deo Ca Group JSC, the project was commenced in 2016.
Costing VND8.51 trillion ($367 million), it was carried out using Vietnamese techniques.
Engineers were allowed to use explosives just twice a day in certain time frames to not disrupt traffic along Hai Van Tunnel 1, a mere 30 meters away.