Tunnels are subterranean marvels that have long fascinated humans. They serve as vital arteries for transportation that connect distant regions and often traverse treacherous landscapes. As technology has advanced, so too has the human ability to construct tunnels of unprecedented length. In this blog post, you will get to know about the world’s longest tunnels, exploring their purpose, construction, and the engineering feats that make them possible. From the depths of mountains to beneath the oceans, these tunnels stand as a testament to human ingenuity and determination. Here is the list of the top 10 longest tunnels in the world.
List of 10 Longest Tunnels in the World
- Delaware Aqueduct
- Päijänne Water Tunnel
- Suzhou Rail Transit Line 3-11
- Dahuofang Water Tunnel
- Orange-Fish River Tunnel
- Bolmen Water Tunnel
- Chengdu Metro Line 6
- Neelum-Jhelum Hydropower Tunnel
- Tunel Emisor Oriente
- Qingdao Metro Line 1
1) Delaware Aqueduct
In New York State, USA, the Delaware Aqueduct is the world’s longest continuous tunnel, extending an astounding 137 kilometers (85 miles) below the surface. This engineering marvel was built in 1945 to meet the increasing demand for dependable, clean water in New York City. The tunnel is part of an extensive water supply system that draws water from the Rondout Reservoir. It supplies over 9 million people in the city and its environs with over 1.3 billion gallons of water daily.
The aqueduct descends to a depth of 750 meters (2,460 feet) in certain places, with a diameter that varies from 4.1 to 4.6 meters (13.5 to 15 feet). Despite its incredible scale and utility, the Delaware Aqueduct has faced some challenges over the years. Leakage was discovered in the late 20th century, with an estimated loss of 20-35 million gallons of water daily. To address this, a $1 billion project was initiated to construct a bypass tunnel to mitigate the leakage, with completion set for 2023.
The Delaware Aqueduct remains a testament to mid-20th-century engineering and continues to play a critical role in sustaining one of the world’s largest urban populations.
2) Päijänne Water Tunnel
At 120 kilometers (74.6 miles) in length, the Päijänne Water Tunnel in Southern Finland is the second-longest tunnel in the world. It was finished in 1982. The purpose of this crucial infrastructure project was to provide over a million people in the greater Helsinki area with clean, fresh water. The second-largest lake in Finland, Lake Päijänne, provides water that the tunnel extracts and transports to treatment plants, where it is treated and then made available to homes and businesses.
Built between 30 and 100 meters (98 and 328 feet) below the surface, the tunnel was painstakingly planned to guarantee stability in the difficult geological conditions of the nation. Its natural gravity allows water to pass through it without the need for energy-intensive pumping systems, making it both extremely effective and environmentally benign. The tunnel is lined with rock and concrete in some sections to prevent seepage and maintain water quality.
The project was also seen as a long-term solution to ensure water security for Finland’s capital, as it taps into one of the country’s most reliable freshwater sources. The Päijänne Water Tunnel remains a key element in Finland’s water supply infrastructure and showcases the country’s forward-thinking approach to environmental management and sustainability.
3) Suzhou Rail Transit Line 3-11
At 86.5 kilometers (53.8 miles), Suzhou Rail Transit Line 3-11 in Suzhou, China, is one of the world’s longest urban rail tunnels. Built between 2019 and 2023, this vast subterranean network was built to accommodate Suzhou’s rapidly expanding population. Suzhou is an important city close to Shanghai. Suzhou is well known for its historic gardens and canals, but as the city grew, more people needed to live there, which made it necessary to build an effective transit system to reduce traffic and meet demand.
The tunnel connects important portions of the city, including its industrial hubs, residential neighborhoods, historical sites, and commercial districts. It spans several lines, including Lines 3 and 4. The ambitious project required advanced tunnel boring machines (TBMs) and modern engineering techniques to navigate Suzhou’s diverse landscape and dense urban environment.
As part of China’s focus on high-speed and efficient urban transportation systems, the Suzhou Rail Transit network now allows millions of passengers to commute quickly and comfortably, reducing travel time across the city. It is also environmentally friendly, contributing to Suzhou’s sustainability goals by offering a greener alternative to car travel and minimizing traffic-related pollution. This tunnel represents a significant leap forward in Suzhou’s infrastructure development and urban mobility.
4) Dahuofang Water Tunnel
Situated in Liaoning Province, China, the 85.3-kilometer (53-mile) Dahuofang Water Tunnel is a wonder of engineering that was finished in 2009. This magnificent tunnel was built as a part of a larger project to alleviate the region’s water problems and guarantee a steady supply of clean water for millions of people living in Liaoning, including important cities like Shenyang.
The tunnel distributes clean water through an underground conduit that passes through a variety of geological formations, including plains and mountains, and connects the Dahuofang Reservoir with an intricate distribution system. Designing the tunnel to pass through these varied terrains while preserving structural integrity and guaranteeing a constant water flow was one of the project’s major problems. Advanced tunneling technology, including tunnel boring machines (TBMs), was used to achieve this.
With a diameter of around 8 meters (26 feet), the Dahuofang Water Tunnel has a massive capacity, transporting approximately 1.5 million cubic meters of water per day. This has been crucial for addressing water shortages in the rapidly developing cities of northeastern China. The tunnel not only secures water resources for residential and industrial use but also plays a vital role in improving agricultural productivity in the region, making it an essential part of China’s water management infrastructure.
5) Orange-Fish River Tunnel
South Africa’s Orange-Fish River Tunnel is a magnificent engineering achievement that was finished in 1972. It is the southern hemisphere’s longest water supply tunnel, spanning 82.8 kilometers (51.45 miles). The tunnel is essential to the flow of water from the Fish River in the Eastern Cape Province to the Orange River, which is the largest river in South Africa. The purpose of this water diversion project is to improve agriculture and irrigation in an otherwise desert location while addressing the region’s ongoing water constraints.
With a diameter of roughly 5.3 meters (17.4 feet), the tunnel is located deep below the earth and relies mostly on gravity flow to minimize the need for energy-intensive pumps. The water transferred through the tunnel supports large-scale irrigation for crops such as citrus fruits, vegetables, and grapes, which are vital for the local economy. It also supplies drinking water to several towns and cities along its path.
One of the significant challenges faced during construction was the diverse and tough geological conditions, but it was completed with advanced drilling techniques. The Orange-Fish River Tunnel remains an essential part of South Africa’s water management infrastructure, providing both economic and social benefits to the region by securing a stable water supply for agriculture, industry, and residential use.
6) Bolmen Water Tunnel
The 82-kilometer (50.95-mile) Bolmen Water Tunnel is situated in southern Sweden. It was finished in 1987. This tunnel is an essential part of the water supply system, carrying fresh water from Kronoberg County’s Lake Bolmen to the densely populated areas of Scania, which include the cities of Lund, Helsingborg, and Malmö. It was built to provide millions of people in southern Sweden, where there were not enough natural freshwater sources to meet the region’s expanding needs, with a reliable and clean water supply.
The system is energy-efficient since the tunnel, which is located well below ground, is gravity-fed, meaning that water flows naturally without requiring a lot of pumping. One of the most notable aspects of the Bolmen Water Tunnel is its environmental sustainability. The project was designed with minimal disruption to the surrounding ecosystem, and the water is delivered with a high degree of purity, needing very little treatment before it reaches consumers.
Maintaining the integrity of this tunnel is a priority for Swedish water authorities, as it plays a key role in the region’s water security. The Bolmen Water Tunnel is not only a technical achievement but also a vital part of Sweden’s long-term strategy to ensure clean and reliable water for future generations.
7) Chengdu Metro Line 6
The huge subterranean transportation tunnel known as Chengdu Metro Line 6, which was finished in 2020, stretches 68.2 kilometers (42.4 miles) through the busy Chinese city of Chengdu. One of the world’s longest metro tunnels, it connects important locations and significantly reduces traffic congestion in this megacity. It is an essential part of the city’s quickly growing metro network. Line 6 greatly enhances urban mobility as it travels from Wangcong Temple to Lanjiagou, passing through residential neighborhoods, business centers, and commercial districts.
Constructed using cutting-edge tunneling technology to negotiate the intricate geological conditions of the city, the tunnel is a marvel of engineering. At peak capacity, Chengdu Metro Line 6 can transport over 30,000 passengers per hour in each direction, making it a key component of the city’s public transport system. The line features cutting-edge train systems and is designed to minimize environmental impact, using energy-efficient technologies.
The construction of Line 6 also highlights China’s focus on enhancing urban infrastructure to accommodate its growing urban population. For Chengdu, a city of over 16 million people, this metro line not only improves commuting efficiency but also supports the city’s economic growth by connecting major urban zones more effectively.
8) Neelum-Jhelum Hydropower Tunnel
As part of the Neelum-Jhelum Hydropower Project, the 68-kilometer (42.25-mile) Neelum-Jhelum Hydropower Tunnel was finished in 2017 and is situated in Muzaffarabad, Azad Kashmir, Pakistan. An essential component of Pakistan’s infrastructure, the tunnel would help the country utilize its rivers’ hydropower potential to satisfy its growing energy needs. Water from the Neelum River is diverted by the tunnel and directed through a system of subterranean tubes to produce power. Afterward, the water is released into the Jhelum River.
This tunnel’s location in a seismically active and geologically complicated area posed significant engineering challenges that called for the use of sophisticated tunnel boring machines (TBMs) and cutting-edge construction methods. Built at a depth of up to 1,500 meters (4,900 feet), the tunnel transfers large volumes of water to power turbines with a capacity to generate 969 megawatts of electricity, which supplies electricity to Pakistan’s national grid.
The project plays a crucial role in addressing the country’s energy shortages by providing a clean, renewable energy source. In addition, it has had a significant economic and social impact on the region, reducing dependency on expensive fossil fuels and promoting energy sustainability in Pakistan. The Neelum-Jhelum Hydropower Tunnel stands as a testament to the country’s commitment to expanding its renewable energy infrastructure.
9) Tunel Emisor Oriente
Completed in 2019, the Tunel Emisor Oriente is a massive subterranean tunnel located in Mexico City that spans 62.5 kilometers (38.8 miles). It is the most significant wastewater tunnel in the world, built to address the long-standing drainage and flooding problems in Mexico City. The city, which was founded on a former lakebed, has long had water management issues because of its basin location and heavy rains throughout the rainy season.
The tunnel is an engineering marvel in one of the most difficult metropolitan settings on earth, with an average depth of 30 to 150 meters (98 to 492 feet). Its diameter of 7 meters (23 feet) allows it to handle over 150 cubic meters of wastewater per second, ensuring that excess rainwater and sewage are efficiently diverted away from the city to prevent flooding. The Tunel Emisor Oriente connects to the Atotonilco wastewater treatment plant, which processes the water before it is reused for irrigation in the nearby Valley of Mexico.
This project addresses the city’s flood risks and improves sanitation, benefiting millions of residents. The tunnel is a key part of Mexico City’s long-term water management strategy, designed to adapt to the growing pressures of climate change and urban expansion.
10) Qingdao Metro Line 1
One of the main components of China’s Qingdao Metro system, Qingdao Metro Line 1 is 59.8 kilometers (37.2 miles) long and was built between 2020 and 2021. This lengthy tunnel greatly improves communication between Qingdao’s central districts and its suburban areas by acting as a vital transit corridor for the coastal city. The metro line travels past significant business, industrial, and residential areas as it travels from Wangjiagang in the north to Qingdao North Railway Station.
Because of Qingdao’s dense urban area and coastline topography, building Metro Line 1 was an intricate undertaking. To guarantee accuracy and safety, sophisticated tunnel boring machines (TBMs) were used during the tunnel’s construction. The tunnel crosses roads, waterways, and heavily populated urban areas below ground. It is designed to handle high-capacity trains, with a maximum speed of 80 kilometers per hour, facilitating the daily commute for millions of residents and easing the city’s traffic congestion.
Besides improving mobility, the project is also environmentally conscious, utilizing energy-efficient train systems and sustainable practices in its construction. As part of China’s broader push to modernize urban transportation, Qingdao Metro Line 1 plays a crucial role in promoting economic growth and urban development, enhancing both the quality of life for residents and the city’s overall infrastructure.
No. | Name of Tunnel | Length |
1 | Delaware Aqueduct | 137,000 m |
2 | Päijänne Water Tunnel | 120,000 m |
3 | Suzhou Rail Transit Line 3-11 | 86,542 m |
4 | Dahuofang Water Tunnel | 85,320 m |
5 | Orange-Fish River Tunnel | 82,800 m |
6 | Bolmen Water Tunnel | 82,000 m |
7 | Chengdu Metro Line 6 | 68,223 m |
8 | Neelum-Jhelum Hydropower Tunnel | 68,000 m |
9 | Tunel Emisor Oriente | 62,500 m |
10 | Qingdao Metro Line 1 | 59,818 m |
Conclusion
As you’ve explored the world’s longest tunnels, you have witnessed the incredible feats of engineering that have made them possible. From the Delaware Aqueduct of New York to the Qingdao Metro Line 1, these structures stand as testaments to human ingenuity and our unwavering desire to connect.
But these tunnels are more than just engineering marvels; they are vital arteries that support global trade, transportation, and tourism. They connect different cultures and economies and foster understanding and cooperation. This blog listed the top 10 longest tunnels in the world.
FAQs
What Is the Longest Tunnel in Asia?
The Zojila Tunnel, currently under construction in India, will be Asia’s longest tunnel at 14.5 kilometers. Built by Mega Engineering and Infrastructure Limited (MEIL), it’s expected to be completed by December 2030 and will connect Srinagar and Leh.
Which Is the Longest Tunnel in Europe?
The Gotthard Base Tunnel in Switzerland is the longest in Europe, stretching 57.1 kilometers (35.5 miles), completed in 2016 for railway transportation.
Which Is the Longest Road Tunnel in the World?
The Laerdal Tunnel in Norway is the longest road tunnel globally, extending 24.5 kilometers (15.2 miles), and it opened in 2000 to connect Laerdal and Aurland.