A parking lot is a location, commonly with a durable or semi-durable surface, that is used primarily for the temporary storage of automobiles and other road vehicles. Parking lots have become a very conspicuous, and increasingly controversial, feature of cities, towns, suburbs and villages of all sizes in which road transport is used. Multi-level parking lots, also referred to as parking structures, have become increasingly common in higher density urban and suburban areas, particularly in the developed countries.
Parking lots and parking structures have proliferated for several reasons. One is the continuing growth in automobile use and thus in the demand for parking space by employees and customers of businesses, particularly in cities or areas where the availability or quality of alternative transportation is poor. A second is that parking lots can be very profitable for their owners because of the often high fees that can be charged for using them, especially in dense urban cores, together with the very low costs of operation.
Another reason is minimum parking requirements, which mandate that all new construction have a certain number of parking spaces per resident or per employee. Such rules began in the U.S. about a century ago and had become nearly universal in that country within a few decades. The result is that typically more than 20 percent of the land area in U.S. central cities is devoted to parking, and often the land area for surface parking used for a building exceeds that for the building itself. Some estimates place the total number of parking spaces in the U.S. alone at two billion, which is roughly equivalent to the land area of the state of Connecticut.1
Although parking lots can be very convenient for automobile users, they also have some major disadvantages that have often been overlooked or ignored. These disadvantages can be broadly classified into damage to the natural environment and damage to urban environments.
Among the former is that parking lots are an important source of pollution. This is caused by rain washing toxic substances leaked from automobiles into the soil and water bodies and sometimes also contaminating the groundwater. The largest volume of these leaking fluids is motor oil, which often contains heavy metals and additional harmful substances. Others include engine coolant fluid, brake fluid, power steering fluid, antifreeze fluid and automatic transmission fluid. Although the leakage from any individual vehicle is usually small, the total effect is large because of the vast numbers of parking spaces throughout the world.
Another source of pollution from parking lots is the toxic coal tar sealants which are still frequently used to coat and repair asphalt surfaces. Moreover, the asphalt itself can leach toxins into the underlying soil, and particles released from abrasion of the asphalt and the markings on it can contaminate the air, soil and water bodies. Parking lots also damage the natural environment indirectly from the toxic emissions from asphalt manufacturing and because of the large amounts of energy required to produce the concrete for multilevel parking structures.
Parking lots can contribute to the creation of heat islands in urban areas because the dark asphalt absorbs and retains more of the sun's energy reaching it than do non-paved areas and because the asphalt and concrete reduce moisture available to cool the air through evaporation. Among the adverse effects of this elevation in temperature are increased discomfort in hot weather and greater energy consumption from the resulting increased use of air conditioning.
Parking lots can also damage the urban environment by making walking less convenient, less pleasant and less safe. This is particularly true in city centers in which large portions of the land area are devoted to parking lots. Moreover, the strong economic incentives to devote land to parking have contributed to the widespread demolishing of centrally located low cost housing and historical buildings and have reduced greenery, thus leaving big gaps in the urban fabric. At the same time, the minimum parking rules greatly increase the costs of land acquisition and/or construction for new residential, commercial and other buildings, thus making urban housing more expensive and increasing the cost of doing business. The various negative effects of large areas of parking lots on housing availability and costs, on walkability, and even on aesthetics, are among the many factors that can encourage people to live in distant suburbs rather than in compact urban areas and thereby increase automobile use.
Fortunately, there has been a growing awareness by city planners and others of the negative effects of parking lots, and thus various techniques are increasingly being implemented to reduce the land and other resources devoted to them. They include discouraging automobile use through tolls and other means, improving alternative transportation, creating pedestrian zones, increasing taxes on parking lots, reducing or eliminating minimum parking requirements, and discouraging the construction of new parking spaces through the establishment of maximum parking rules.
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1. Nathaniel Meyersohn, "This little-known rule shapes parking in America. Cities are reversing it," May 21, 2023, https://www.cnn.com/2023/05/20/ business/parking-minimums-cars-transportation-urban-planning/index.html