List of longest tunnels

Columns: Type | Name | Location | Length | Year | Comment
Water supply | River Arpa - Lake Sevan tunnel | Armenia ( at the time of construction Soviet Union ) | 48,314 m ( 30.0 mi ) | 1981 | Longest tunnel built to restore ecological balance . Transfers water from Arpa River to the Lake Sevan to recover its level | Metro | Seoul Subway : Line 5 | Seoul , South Korea | 47,600 m ( 29.6 mi ) | 1995 | Longest metro/rapid transit tunnel until Guangzhou Metro Line 3 extension opened in 2010 | Water supply | Pahang - Selangor Raw Water Transfer Project | Pahang & Selangor , Malaysia | 44,600 m ( 27.7 mi ) | 2014 | 5.2 meters in diameter | Metro | Mass Rapid Transit ( Singapore ) : Downtown Line | Singapore , Singapore | 43,700 m ( 27.2 mi ) | 2017 | Longest rapid transit line in South East Asia | Water supply | # 1 Tunnel , Yellow River Diversion to Shanxi North Line | Shanxi , China | 43,670 m ( 27.1 mi ) | 2011 | See South-North Water Transfer Project | Water supply | # 7 Tunnel , Yellow River Diversion to Shanxi South Line | Shanxi , China | 43,500 m ( 27.0 mi ) | 2002 | See South-North Water Transfer Project

Example questions:
How long is the River Arpa - Lake Sevan tunnel that is situated at an altitude of 1,900 m ? | What is the length of the Delaware Aqueduct which was built between 1939 and 1945 ? | What is the length of the second longest tunnel in the world , the Päijänne Water Tunnel ? | What is the length of the Mass Rapid Transit ( Singapore ) , Downtown Line ?

Answers:
48,314 m ( 30.0 mi ) | 137,000 m ( 85.1 mi ) | 120,000 m ( 74.6 mi ) | 43,700 m ( 27.2 mi )