From this aerial view, you can see how commercial airports may require a little bit of room to spread out.

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Wanted Since the 1950s: Airport Sites

Commercial airports require huge amounts of land for runways and other facilities. As a result, few have been built in North America and Europe since the 1950s because metropolitan areas simply don't have any suitable sites. Even airports built on the outskirts of a city in the 1950s now find themselves hemmed in by urban and suburban development. This leaves planners with no choice but to renovate existing structures or expand within long-established property lines.

With that said, some cities have managed to add a commercial airport in the last couple of decades. Denver, for example, began construction of its international airport in 1989 and, after numerous construction delays, opened the facility in February 1995. Since then, it's grown to be the fifth-busiest airport in the United States, with more than 145,000 passengers passing through its gates each day [source: Denver International Airport].

Building a commercial airport on the scale of Denver's requires years of planning and a number of complex decisions. Here are some of the things airport planners must consider:

  • Air transportation forecast: Planners use computer simulations and predictive modeling to make forecasts about an airport's anticipated traffic. They need to account for the number of arrivals and departures on a daily basis, but they also need to know the size of the aircraft that could potentially use the facilities because larger aircraft require longer runways. For example, large jets such as the Boeing 747 or Airbus A380 need about 10,000 feet (3,300 meters) to take off [source: Bowen and Rodrigue]. Based on this forecasted demand, planners make recommendations about the number and length of runways, as well as the size of airport terminals, all of which determines the amount of land required for a feasible project.
  • Site location: As we've already mentioned, most commercial airports are located near major cities so workers and passengers can get to the facility easily. And yet most metropolitan areas have little or no land available for development on such a large scale. To find a site that can accommodate current needs and future growth, planners may seek property on the outskirts of a city, especially if rail and highway systems can provide adequate service between the airport and downtown areas. The tradeoff, of course, is availability of land. The Denver airport is almost 25 miles (40 kilometers) outside the center of the city, but the site gives planners a significant amount of elbow room. In fact, with its 53 square miles (137 square kilometers) of land, Denver International Airport is the largest airport in North America and the second-largest in the world (as of press time), with room enough to add six additional runways, another terminal and two additional concourses [source: Denver International Airport].
  • Altitude: An airport's elevation can have an impact on its overall design. Air density is lower at high elevations, so longer runways are needed for an aircraft to achieve the necessary lift. Denver International Airport sits 5,431 feet (1,655 meters) above sea level, making it one of the highest airports in the U.S. Airfields in other countries must accommodate even higher elevations. For example, some South American airports, located in the Andes Mountains, are almost three times higher than Denver's.
  • Topography: Runways require a smooth, level landscape with no obstructions. Planners must find naturally flat areas of land, or they must make them so by flattening hills or filling in swamps. These latter activities can increase construction costs considerably.
  • Meteorological conditions: Airports built near an ocean experience much different weather patterns than those located inland or in mountains. For example, pilots flying into San Francisco's airport must often deal with thick banks of fog. In Orlando, they may deal with towering thunderstorms and wind shear. Airport planners must account for prevailing weather conditions when laying out runways and other structures.
  • Environmental impact: Airports can have a lasting impact on the environment. They produce air and noise pollution and can impinge upon wetlands and rivers. The planning process often requires years of negotiation and stakeholder engagement to find and approve a site that satisfies the needs of community members (or at least a majority of them).

Once a site is chosen, planners must then design and lay out the airport's major structures. Much of their efforts center on how to best configure runways and terminals for the most efficient flow of traffic on the ground and in the airspace during departures and landings.