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.
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.
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.
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 to avoid ruining the illusion that is being created.
According to modern legend, Walt Disney was bothered by the sight of a cowboy walking through California Disneyland's Tomorrowland en route to his post in Frontierland. He felt that such a sight was jarring, and detracted from the guest experience. When a new Florida Disney park was being planned, engineers designed utilidors to keep park operations out of guests' sight.
The utilidors are beneath the Magic Kingdom in Florida, but they are not a basement. Because of an elevated water table, most of these tunnels were actually built at ground level, and the Magic Kingdom was built above that. All the guests of the park see streets that are elevated by one story. Parts of Fantasyland, including the Cinderella Castle, are at third-story-level (this is why the Castle seems to loom so large as guests approach it via Main Street, USA). The ground's incline is so gradual that guests do not realize they are ascending to the second and third stories. The Magic Kingdom is built upon soil which was removed from what is now the Seven Seas Lagoon.
The utilidors are built on 9 acres (36,000 m2), and the floor plan is a circle with a path down the middle. The tunnel walls are color-coded to make it simple for cast members to determine their location. The utilidors can be accessed from a main tunnel entrance located behind Fantasyland, or through unmarked doors throughout the Magic Kingdom. Magic Kingdom cast members park about one mile (1.6 km) away and are transported via a Disney bus to the tunnel. Some shops, restaurants and attractions have direct access to the utilidors.
Cast members navigate the tunnels on foot or in battery-operated vehicles that resemble golf carts, which cast members call "Pargos". Gasoline-powered vehicles are not allowed in the utilidors, with the exception of armored cash pickup trucks and, in extreme emergencies, ambulances.
The utilidors have been referred to as an "underground city", the functions of which include:
- Waste removal: The Magic Kingdom uses an automated vacuum collection (AVAC) system for waste removal. Sanitation crews remove trash from the park twenty-four hours a day, and dump it into AVAC system processors throughout the park. The trash then travels through pneumatic tubes to a central location where it is processed, compressed, or recycled.
- Electrical operations: The park's computer system, the Digital Animation Control Systems (DACS), is operated and monitored from control rooms in the utilidors. This system monitors everything in the park, from sound systems to attractions, Audio-Animatronic figures to parades, fire prevention and security systems to cash registers.
- Deliveries and storage warehouses: Deliveries are received, processed, and stored at the utilidors until use. This ensures that guests do not see delivery trucks, nor do they see cast members carting merchandise through the park.
- Food service: The park's cooking and prep kitchens are housed in the utilidors.
- Costuming: For years, the park's costuming department (for cast members and Audio-Animatronic figures) was located in the utilidors. Over 1.2 million costumes were housed here, making it the largest operating wardrobe department in the world. In 2005, Disney replaced this facility with a larger location in the cast member parking lot.
- Cast member services: Separate locker rooms for men and women are located in the utilidors, as well as cast member cafeterias. There is also a check cashing service, an employee hair salon called "Kingdom Kutters," rehearsal rooms, and administrative offices.
In 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.
In industrial, institutional, and municipal environments
|This section requires expansion. (April 2013)|
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.
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.|
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 and Sonshan MRT rapid transit lines in Taipei, Taiwan
- Azabu-Hibiya Common Utility Duct in Tokyo, Japan
- Minatomirai District lines in Yokohama, Japan
- 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.
- Poundbury Village in Duchy of Cornwall, Prince Charles' master planned community in England incorporates common utility ducts
- German cities such as Bremen. This city has near perfect surfaces on its footways, cycleways and streets. Virtually no repairs or disturbances are visible. The number of streetworks in progress is trivial. This can only be achieved by (a) vehicles not driving on footways or cycleways (b) utility ducts making it unnecessary to disturb the surfaces in order to access the networks below for repairs, maintenance and alterations. Utility networks are housed in a cluster of pipes which are located under footways and cycleways.
- The Dartford Cable Tunnel allows high voltage electricity line to cross the River Thames.
- "National Grid - Overview - Why a tunnel?". National Grid plc. Retrieved 2013-03-30.
- "Betcha Didn't Know (World View) by Mark Goldhaber on September 11, 2003". Mouseplanet.com. 2003-09-11. Retrieved 2010-06-07.
- "Fun Facts of Magic Kingdom's Underground Complex". Hiddenmickeys.org. Retrieved 2010-06-07.
- MAA Website
- BigEmpire.com Website
- Yokohama Landmark Building Website
- Mitchell, Sandy. "Prince Charles is not your typical radical." National Geographic. May 2006.  Accessed online 9/14/06
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