The Hải Vân Tunnel, the longest tunnel in Indochina at 6.28 km (3.90 mi), lies on Highway 1 between the two cities of Da Nang and Huế in central Vietnam.
The Hải Vân Pass has long been recognised as a major bottleneck. The concept of a tunnel to bypass the long route over the top had long been sought.
Route planning and design work started in January 1998 by a joint venture between Nippon Koei Company Limited Japan and Louis Berger International Inc., USA with the Vietnamese Transport Engineering Design Incorporated (TEDI) providing consultation on the project.
The tunnel was split into two segments, a southern and a northern section. The southern section (4 km/ 2.49 mi) was constructed by a Vietnam–Japan joint venture between the Japanese Hazama Corporation and their Vietnamese partners, Cienco 6. The 2 km (1.24 mi) northern section was constructed by a joint venture between Korea's Dong Ah construction company and Vietnam's Song Da Construction Corporation.
The tunnel officially opened on June 5, 2005. The main tunnel is 11.9 m (39.0 ft) wide. A second tunnel running alongside the main tunnel is currently used for maintenance and emergencies but it is planned to expand this at a later date as traffic increases. It is connected to the main tunnel by 15 cross-tunnels. The tunnels have lighting, fire alarms, communication, water supply and treatment, ventilation fans, and radio broadcast systems.
Currently the single tunnel has one lane of traffic in each direction. As no overtaking is possible this can result in minor delays if motorists are stuck behind slow moving traffic. Motorcycles, cycles and pedestrians are not allowed in the tunnel but a new shuttle service began in November 2006. A small waiting area has been established at each end of the tunnel where visitors can take photographs and watch a documentary about the making of the tunnel.
The tunnel reduces the distance between Da Nang and Huế by 20 km (12 mi) and saves between 30 minutes and an hour on traveling times over the old Hải Vân Pass route.
The tunnel subsequently has received an award for quality by the American Construction Management Association.