Archaeology is continually pushing the dates back for the first discovered usage of drains and sewers in ancient communities and it is clear that such structures were a part of many early civilizations. Often, the earliest examples were surface troughs, perhaps covered over with stone slabs. Evidence of early water pipes and tunnels can also be found – used for convenience of water distribution but also for maintenance of a water supply in case of hostilities. The Greeks and the Romans both built tunnels for transportation purposes and, in the late 1400s, Leonardo da Vinci was already sketching ideas for three-dimensional cities with canals and roadways on different levels. Paris and London started to develop modern sewer systems in the 1800s. London was the site of the first shield tunnel under a river completed in 1843 and the first subway (metro) system completed in 1863. Paris and New York followed with the start of their metro systems in the early 1900s and Moscow in the 1930s. New York was also an early leader in the placement of electrical lines underground in the early 1900s and has a current length of underground cable estimated at 146,000 km (91,000 miles). Gas lines were being placed underground by the early 1800s and telephone lines followed in the late 1800s. More recently, the number of utility lines being placed underground has increased rapidly especially in those countries that have privatized utility services and allowed competition among multiple providers of the physical utility networks. In the U.S., for example, it is estimated that over 5.6 million kilometers (3.5 million miles) of underground utility services exist .One would imagine with the long history of underground use in urban areas, the huge and rapidly growing investment in underground facilities and the increasing congestion of urban underground space – particularly beneath public rights-of-way – that great care would be taken in planning how this space is used both now and in the future. In most cities, this is very far from the true situation.
REVITALIZATION OF A CITY
Very few cities in the world have been planned from scratch and very few cities in the world are willing to abandon their heritage of urban form and historic buildings to improve transportation, public amenities, utility services and other forms of improved commerce and quality of life. Placing new city functions such as transportation and commercial and storage facilities underground provides a new mobility and commercial potential to a city but without destroying the surface environment. While individual projects may move underground because of particular difficulties or the impossibility of a surface solution, it is rare that cities plan comprehensively to use the underground for urban revitalization.
GROWTH OF A CITY
Cities that are not planned from scratch do not start out as cities but grow from small settlements into towns and from towns into cities and large conurbations. In a small village even today, the use of the underground is minor and not particularly congested. Water, sewer and gas will be underground and perhaps electrical and telecommunications services. Very little else will have the reason to be placed underground. In a large city, however, the pressures are very different. Land is scarce and valuable; transportation problems increase, and land uses change over time. It is not difficult to predict or to track by looking at other cities that the underground can be a valuable tool in addressing these problems as a city grows. However, it seems almost impossible to introduce the concept of underground planning to a growing urban area at a time when it could make a significant difference to future costs and effective utilization.
Underground utility and transportation services provide service functions or the “infrastructure” of a city and as they multiply it becomes more difficult to find the clear space for new services and structures without extending deeper and deeper below ground. Extending underground structures to lower levels not only typically increases costs but also makes most underground facilities less useful in terms of supporting urban life and commerce. Tokyo, for example, has progressively used deeper and deeper structures below ground with 5 levels of metro lines in some areas and planning for new road and metro lines at depths exceeding 50 m.
The underlying problem with this progressive and usually piecemeal growth is that many earlier uses of the underground either preclude later uses or make them far more difficult to construct and/or less beneficial in their contribution to solving urban problems .
NEED FOR PLANNING
If underground facilities are to provide the most valuable long term benefits possible, then effective planning of the underground resource must be conducted. Unfortunately, it is already too late for the near surface zones beneath public rights of way in older cities around the world. The tangled web of utilities commonly found is due to a lack of coordination and the historical evolution in utility provision and transit system development. The underground has several characteristics that make good planning especially problematical:
- Once underground excavations are made, the ground is permanently altered. Underground structures are not as easily dismantled as surface buildings.
- An underground excavation may effectively reserve a larger zone of ground required for the stability of the excavation.
- The underground geologic structure greatly affects the types, sizes, and costs of facilities that can be constructed, but the knowledge of a region's subsurface can only be inferred from a limited number of site investigation borings and previous records.
- Large underground projects may require massive investments with relatively high risks of construction problems, delays, and cost overruns.
- Traditional planning techniques have focused on two dimensional representations of regions and urban areas. This is generally adequate for surface and aboveground construction but it is not adequate for the complex three dimensional geology and built structures often found underground. Representation of this three dimensional information in a form that can readily be interpreted for planning and evaluation is very difficult.
GROWTH OF TRENCHLESS TECHNOLOGIES
There are potential problems that may derive from the widespread adoption of trenchless techniques. These are mostly long-term and avoidable with good planning. For example, trenchless installation techniques for cables and conduits allow new systems to be installed relatively easily by passing beneath existing systems and, for safety reasons, it is often prudent to allow significant clearance to existing systems. This will lead to a tendency for utility systems to gradually occupy larger and larger zones of the urban underground and to follow curved rather than straight alignments. The privatization and duplication of utility systems that is occurring in many countries also increases the pressure on available underground space and could accelerate this trend.
Over time, this spreading use and less predictable location will affect the cost and feasibility of installing later utilities or other urban systems such as transit and road tunnel systems or urban underground space for commercial or service purposes. To avoid these problems and to take full advantage of the characteristics of trenchless installation and repair will require more comprehensive planning of how underground utility systems are to be provided in urban areas than has been the case in the past.
VALUE OF UNDEGROUND SPACE
Use of the underground in the past has been based mostly on a first come, first served basis with principal attention focused on minimizing the cost of that increment of underground development. Space allocation for shallow utilities beneath roadways is practiced, but examples of more comprehensive utility planning are more difficult to find.
Does the fact that public agencies and utilities do not have to pay for utilizing the public space beneath rights-of-way mean that the space should be administered as if it has no value and no impact on the long-term development of the urban area? In effect, this is what often happens at present -- current projects to be placed beneath streets are laid out and constructed on the basis of avoiding existing utilities, maintaining access for future repair, minimizing damage to boulevard trees, and where possible following utility layout corridors which have been set up to reduce future utility conflicts and accidental damage due to unknown location. It is desirable to build underground facilities as cheaply as possible so that they can be used economically to solve urban problems. If no value is assigned to space underground, however, there are none of the normal economic pressures to help rationalize the appropriate use of the underground and minimize the volume of this resource usurped by individual uses. These issues present difficult problems to resolve, especially in older portions of cities with narrower streets and a longer history of utility development. The nature of the decisions currently made however do not consider substantially alternate uses of the space which may be desirable later in the growth of the urban area.
ARE THERE GOOD EXAMPLES OF UNDERGROUND PLANNING?
There certainly are good examples of cities and regions that have addressed the issues of underground planning. Scandinavia has a number of cities that have done extensive underground planning, made provision for the progressive collection of a public database of underground conditions and practices space reservation policies for future underground facilities. France has a long tradition of thinking about urban underground space use having started an organization in the 1930s that discussed the future of urban underground development. Russian and Eastern European cities used their central planning powers to develop common utility galleries or utilidors. Japan has investigated underground space use as an important topic since the early 1980s. The author was involved for 25 years in the planning for future underground space use in the Minneapolis-St. Paul area of the U.S.
If one were to approach the people involved in this work, however, to ask them to evaluate the continued and long-term effectiveness of their work, I believe that they would express disappointment with the extent of impact on planning decisions – particularly as individuals change in the decisionmaking positions. The French group of the 1930s essentially disappeared with their ideas to be “rediscovered” later in the century. Minneapolis undertook some city-wide underground space planning in the 1980s with some notable achievements in space reservation and impact on project designs at the university, airport and other critical locations but without creating an ongoing underground planning effort. After a 2-year study of the use of underground space use in urban areas in Australia , in which the author was involved, the City of Sydney indicated that it would undertake a comprehensive underground space use planning effort for the city. However, it is the author’s understanding that, as the key individuals moved positions, the impetus for such a study was lost.
CAN WE PROVE THAT UNDERGROUND STRUCTURES ARE WORTH THEIR COST?
Underground transit systems, underground road tunnels and other major underground developments are expensive and can be financially risky endeavors. So, naturally, planners and politicians want reassurance that they are making the right decision. Also, in many cases, there will be other backers of alternate plans with different sets of costs, urban impacts and constraints.
One of the more frustrating aspects of studying underground space use is the difficulty of providing quantitative information on the benefits of using underground space in terms of urban revival, environmental benefits, time savings, etc. Often, the benefits of a project are very clear in a general way. For example, the relocation underground of the waterside road in Oslo city center has encouraged and allowed major redevelopment of the harborside area as well as provided public open spaces in the center of city. The tearing down of the elevated Embarcadero freeway in San Francisco released a surge in property values and desirability of properties in the neighborhood. The original Boston Artery project considered an underground scheme in the 1950s only to reject it on the basis of increased cost. In the 1990s, the new project to replace the elevated artery with an underground tunnel started with an estimated cost orders of magnitude higher than the differences in the costs of the initial project alternatives.
Yet, with such important urban decisions, can we access the data needed to make an intelligent decision? The answer in most cases is no – typically there is information on costs of underground solutions available but there is very little reliable information on benefits. Also, projected project cost information often is distorted according to the interests of the backers of alternate project schemes. This may include both unrealistically high and low estimates of the cost of the underground works. Increase in real estate values in the vicinity of underground projects is often a real financial benefit that is significant when related to project costs but it is very difficult to find good data in this area. For example, if land costs increase 20% in a one square kilometer city area where land costs US$5,000 per square meter, the added value in land cost alone is US$1 billion. The impact on total building real estate value could be much higher.
HOW CAN UNDERGROUND PLANNING BECOME AN INTEGRAL PART OF URBAN PLANNING?
In the authors’s view, the ongoing problems of underground planning stem from the following issues:
- Urban underground planning is not widely practiced and it is rarely a part of curricula for undergraduate students in underground planning. Hence, very few planning professionals are exposed to the need for underground planning and the issues involved.
- Planning and architectural undergraduate curricula are tending to spend less time on engineering and technical issues that affect planning and design. Hence, they do not have an understanding of the geological and engineering issues that control underground space use.
- The people who understand the potential benefits of underground projects the best are tunnel and underground construction experts who are perceived to have a self interest and hence their objectivity is questioned.
There is very little systematic collection of data on the impact of underground projects on the area that they serve.
To redress these problems, it is suggested that:
- Cities and regional governments should be strongly encouraged to add underground planning to their two-dimensional surface planning efforts. The underground is an important urban resource and it is irresponsible not to include it in city planning.
- Schools of planning should be challenged not to ignore the space beneath cities and the underground infrastructure that serves cities. Many of the urban challenges of the future involve maintaining and revitalizing existing urban areas. Effective use of the underground can be a key tool in this regard.
- Major underground projects with a likelihood of significant urban design, land value and environmental impacts should include a component to study the impact of these changes or at least to create the baseline by which future studies can measure the impact. Such data needs to be published in the international literature where it is accessible for use in decisionmaking on other projects.
- The subsurface engineering community needs to reach out and find planners, economists, real estate specialists, urban design specialists, etc. who are interested and willing to participate in research on these topics. Their input is essential both in terms of ensuring validity of the data and having the means of transferring the information to key decisionmaking personnel.
APPENDIX: INTERNATIONAL TUNNELLING ASSOCIATION SUBSURFACE PLANNING POLICY STATEMENT
The Working Group on Subsurface Planning of the International Tunnelling Association prepared in 1990 the following policy statement on the needs and benefits for planning of subsurface uses.
The subsurface should be considered a resource for future development in the same way as surface land or recoverable minerals and the use of this resource should receive careful planning to ensure that the resource is not damaged or usurped by uncoordinated first uses.
Once an underground opening is created, the ground can never be restored to its original condition and the presence of this opening will affect all future uses of the subsurface in its vicinity. Geological conditions vary greatly - favorable conditions allowing less expensive underground construction should be identified. These factors place a heavy emphasis on responsible planning for all uses of the underground.
It is important that the awareness of the underground option among planners, developers and financiers be increased so that subsurface planning issues are properly addressed.
National, regional and local policies should be prepared to provide guidelines, criteria and classifications for assessing appropriate uses of underground space, identifying favorable geological conditions, defining priority uses, resolving potential use conflicts and establishing site reservation policies for important future uses.
It is recommended that every region or city establish a permanent record keeping system for the maintenance of detailed records of the use of the subsurface. This record keeping should be coordinated by a single agency to ensure compatible and complete records and should include "as built" records rather than project plans. Records should include activities which affect the potential use of the subsurface which may not be classed as specific subsurface facilities (e.g. groundwater extraction and deep piles for buildings and groundwater extraction).