Vast communication, power, water, and transportation networks are required to support the daily lives of city populations; and, the high density of urban living can make it possible to use these systems more efficiently.
Above ground, highways, rail lines, streets, and sidewalks provide pathways for residents to move from place to place. Within most central business districts, public transportation networks are heavily traveled, although many streets and highways within these areas can also be characterized by heavy congestion. And, while a city's utility and transportation infrastructure can extend out to the surrounding suburbs, so can the various emissions from these same systems.
Under the streets of most large urban areas is a complex system of columns, pipes, and tunnels that helps to support city life. These networks conserve valuable space above ground while holding up city buildings and bridges, supplying water, disposing of sewage, and protecting electrical wires, natural gas pipelines, and telecommunications cables from the elements. Most importantly, development of underground sewer systems led to significantly improved sanitation and public health for city residents.
There have been substantial advances in tunnel building technologies over the last century, but underground city infrastructure date back thousands of years. Evidence suggests that ancient cities in India, Egypt, and Greece used bathrooms and sewers more than 4,000 years ago. Roman sewers, called cloaca, were made as early as 300 B.C. and served as models for the sewage systems built in Europe during the nineteenth century.
Prior to the use of highly-engineered and organized sewage systems, many European cities utilized underground networks for water supply and to drain rainwater, but relied on cesspits as a primary means of waste disposal. These early underground systems often flooded, leaking waste into city streets and local waterways which brought forth issues of pollution and disease. To alleviate these concerns, large cities in Europe and North America began to construct new sanitary systems by the late 1800s.
Unfortunately, many of these underground systems, particularly in the older cities along the eastern coast of the U.S., are more than a century old and maintenance and repair is both costly and time consuming. According to the New York City Department of Environmental Protection, one-tenth of all of New York City's water flow is lost through leaking water mains. In both New York and Washington, D.C., faulty systems have been a source of exploding manhole covers causing power outages, traffic jams, and subway delays. The built environment above ground, which significantly increases both cost and difficulty, is the main hindrance in putting in new systems; any replacement would also cause a major disruption to daily life in these large cities. Circumstances, such as these, have led many city governments to continue fixing their aging systems.
Urban Mobility Information The Texas A&M University's Texas Transportation Institute works in cooperation with departments of transportation from all over the U.S. to produce an annual report on the escalating congestion in U.S. cities.
National Geographic: New York Underground This site graphically explains what can be found under the streets of New York City by means of taking a "core sample" and describing each of the layers. Especially interesting are the photographs of some of the activities that take place beneath the city, including the subway and deep-water tunnels.