Utility tunnel

A utility tunnel, utility corridor, or utilidor is a passage built underground or aboveground to carry utility lines such as electricity, water and sewer pipes. Communications utilities like fiber optics, cable television and telephone cables are also sometimes carried. They may also be referred to as a services tunnel, services trench, services vault, or cable vault. Smaller size cable containment is often referred to as a cable duct, or underground conduit. Direct-buried cable is a major alternative to ducts or tunnels.

Usage

Utility tunnels are common in very cold climates where direct burial below the frost line is not feasible (such as in Alaska, where the frost line is often more than 18 ft (5.5 m) below the surface, which is frozen year round). They are also built in places where the water table is too high to bury water and sewer mains, and where utility poles would be too unsightly or pose a danger (like in earthquake prone Tokyo). Tunnels are also built to avoid the disruption caused by recurring construction, repair and upgrading of cables and pipes in direct burial trenches.^[1]

Utility tunnels are also often common on large industrial, institutional, or commercial sites, where multiple large-scale services infrastructure (gas, water, power, heat, steam, compressed air, telecommunications cable, etc.) are distributed around the site to multiple buildings, without impeding vehicular or pedestrian traffic above ground. Due to the nature of these services, they may require regular inspection, repair, maintenance, or replacement, and therefore accessible utility tunnels are preferred instead of direct burying of the services in the ground.

Utility tunnels range in size from just large enough to accommodate the utility being carried, to very large tunnels that can also accommodate human and even vehicular traffic.

Industrial, institutional, and municipal environments

Utility tunnels are often installed in large industrial plants, as well as large institutions, such as universities, hospitals, research labs, and other facilities managed in common. Shared facilities, such as district heating, use superheated steam pipes routed through utility tunnels. On some university campuses, such as the Massachusetts Institute of Technology, many of the buildings are connected via large underground passages to allow easy movement of people and equipment.

Some municipalities, such as Prague in the Czech Republic, have installed extensive underground utility tunnels, to allow installation and maintenance of utility lines and equipment without disrupting the historic streets above.

Utility tunnels may attract urban explorers, who enjoy investigating hidden complex networks of spaces.

At Walt Disney World

Some of the largest and most famous utility tunnels are at Disney theme parks. They were first built for Walt Disney World's Magic Kingdom in Florida. Smaller utilidor systems are built under the central section of Epcot's Future World, primarily beneath "Spaceship Earth" and "Innoventions," and at Pleasure Island. Disneyland also has a small utilidor through Tomorrowland. The utilidors are a part of Disney's "backstage" (behind-the-scenes) area. They allow Disney employees ("cast members") to perform park support operations, such as trash removal, out of the sight of guests.

Arctic towns

Utilidors are above-ground enclosed utility conduits that are used in larger communities in the northern polar region where permafrost does not allow the normal practice of burying water and sewer pipes underground. They can in particular be found in Inuvik, Northwest Territories and Iqaluit, Nunavut. Not all older homes are connected, and these must rely on trucks to deliver water and remove sewage. Most homes in rural Alaska (off the road system) are not equipped with plumbing and require fresh water and waste to be transported by personal vehicle such as snowmobile or four-wheeler ATV. Villages with utilidors are considered more advanced.

Utilidors may also be used to carry fuel lines, such as natural gas. They are not normally used to carry wiring for electric, telephone and television service, which are usually suspended from poles.

Comparison with direct burial of utilities

The advantages of utility tunnels are the reduction of maintenance manholes, one-time relocation, and less excavation and repair, compared to separate cable ducts for each service. When they are well mapped, they also allow rapid access to all utilities without having to dig access trenches or resort to confused and often inaccurate utility maps.

One of the greatest advantages is public safety. Underground power lines, whether in common or separate channels, prevent downed utility cables from blocking roads, thus speeding emergency access after natural disasters such as earthquakes, hurricanes, and tsunamis.

The following table compares the features of utility networks in single purpose buried trenches vs. the features of common ducts or tunnels:

Trench (direct burial)	Duct (or utility tunnel)
Long-term collaboration has not always been a high priority. Robust, precise location records for older utility trenches were often not provided or maintained, and older trench locations are often unknown.	Ducts are often used where developing authorities value the long-term benefits of utility co-location. That focus on long-term collaboration often includes greater emphasis on making duct locations easily known.
Single-purpose trenches encourage a utility to follow a single-minded route to shorten runs and save initial installation costs for that particular utility. But uncoordinated routing encourages spatial chaos, using more space than if trenches were highly parallel, and greatly increasing the overall encumbrance on surrounding development.	Ducts demand coordinated, highly collinear routing, reducing the overall encumbrance on surrounding development.
Even if parallel, trenches occupy more surface area. The surface area they use encumbers the area available for all forms of property development and construction with the burden of avoiding or moving the utilities.	Ducts are typically cylindrical, greatly increasing the volume of network resources per unit of surface area occupied.
Access to a trenched network typically requires locating the utility network, cutting open the road or pavement surface, breaking open the concrete platform and excavating a trench, followed by reinstatement of the trench, concrete platform and road surface afterwards. (This is where most of the financial cost of network renewals and maintenance is incurred.) Road surfaces can be seriously damaged by frequent trenching, requiring more frequent resurfacing. In the process, pavement slabs are often broken and badly aligned. UK roads are subject to 5 million roadworks per year (mainly for utility works).	Utility networks in ducts typically include designed-in access points (like those now used by British Telecom). Where ducts and access points are installed, excavations are rare and recurring maintenance costs are lower.
Maintenance of networks in trenches requires re-digging and restoring the trench and any roadbed above it. Road users suffer repeated delays from roadworks, particularly in dense cities. Roadworks for trench adjustments also require large quantities of sand, aggregate, cement, tarmac and marking paint.	Ducts allow maintenance through their access points. Since access points mostly obviate new roadway intrusions, traffic delays from duct-related roadworks are greatly reduced. Not disturbing roadways means network adjustments require materials only inside the ducts.
Rural properties are often denied access to gas or cable telecom because the cost of new trench deployment cannot be economically justified independently of other networks. Rural networks for electricity and telecoms are often above ground, with increased risk of disruption, even though there are usually local underground water and gas networks serving the same properties.	Sharing the higher initial installation cost of ducts across all services could make rural service more economically feasible. Where ducts are used, all networks are typically underground in multi-purpose ducts. Redundant above-ground electricity and telecom poles are usually dismantled, increasing safety and reducing natural disaster impacts.
Without common utility ducts, new types of networks require new trenches or independent ducts. Such expansions have already included cable telephone and television networks. Proposed local heat transfer systems and more localised, reconfigured power generation systems would also require new trenches.	Common utility ducts are designed to accommodate anticipated new and evolving networks.
The high thermal conductivity of soil would require extreme insulation for heat transmission through trenched networks.	The low thermal conductivity of air in ducts allows heat transmission with less insulation and cheaper standoffs.

Examples

Many examples of utility tunnels are found in Japan, where government officials have sought ways to reduce the catastrophic effects of earthquakes in their tectonically active country. Their use, however, is not limited to that country and there are many examples of such utility tunnels. These include:

Incorporated with Xinyi^[2] and Sonshan MRT rapid transit lines in Taipei, Taiwan.^{[citation needed]}
Azabu-Hibiya Common Utility Duct in Tokyo, Japan^[3]
Minatomirai District lines in Yokohama, Japan^[4]
Portions of the Chicago Tunnel Company's abandoned network of tunnels are leased to utility companies for use as common utility ducts for electrical, communication and HVAC lines. The tunnels lie approximately forty feet below the street surface and run under all streets in the central business district, except where they were displaced by rapid transit tunnels.^{[citation needed]}
Poundbury Village in Duchy of Cornwall, Prince Charles' master planned community in England incorporates common utility ducts^[5]
Bremen, Germany has near perfect surfaces on its footways, cycleways and streets, with virtually no visible repairs or disturbances. This is achieved by an absence of vehicles on footways or cycleways, and utility ducts that make it is unnecessary to disturb the surfaces in order to access the networks. Utility networks are housed in a cluster of pipes which are located under footways and cycleways.^{[citation needed]}
The Dartford Cable Tunnel allows high voltage electricity line to cross the River Thames.^{[citation needed]}
The Utility Tunnels in Qatar built on the Lusail, 15 km north of Doha, is approximately 14~15 km in length.^{[citation needed]}
The old Beacon Hill Tunnel in New Kowloon, Hong Kong, a disused railway tunnel which now carries a towngas pipeline
Tunnels of Hongkong Electric^[6]
Utility Tunnel in GIFT City, Gandhinagar, India^[7]

Gallery

Stark utility tunnel in Zurich, Switzerland
District heating tunnel beneath the Rhein River in Cologne, Germany
District heating tunnel in Copenhagen, Denmark
Red arrow marks a prefabricated element of a utility tunnel already placed in the trench
A newly built utility tunnel in Haifa, Israel
Tunnel in Prague is shared by pipes and cables
Utility passageway between two buildings of a Ballistic Missile Early Warning System site in Alaska.
Utilidors connecting houses in Inuvik, Northwest Territories, Canada
Utility Tunnel in GIFT City Gandhinagar, India
A utilidor system is used in Barrow, Alaska due to extensive permafrost underlying the city. At right foreground is a portion of the utilidor crossing Okpik Street overhead, adjacent to Barrow High School.