I recently reviewed some plans for a proposed new apartment complex in Durham, NC. I was surprised to see that the footprint of the building accounted for only 36% of the area of the project—the remainder consisting of parking for the residents. Both the building and the parking area will contribute to the increasing area of impervious surface that covers the Earth—meaning the area that is devoid of nature and does not allow any infiltration of water to the soil.
This gave me pause to ask, what is the area of impervious surface of the world, how much of that is contributed by cities, how much by roads, and how much by parking areas for cars. A quick search on the web indicated that urban area tops the list, roughly estimated at 300,000 km2 in the United States. Roads are next at 40,000 km2 of area in the U.S., about 0.4% of the land. It is noteworthy that 83% of the United States is within 1 km of a road.
Here, I calculate the area of parking as a new statistic. There are more than 1.44 billion automobiles in the world, of which 290 million (20%) are in the U.S. Assume the average parking place is 8 x 18 feet, amounting to 13.4 m2. So, the total fleet of cars in the United States could be parked in a single lot of 3880 km2—about 10% of the area of the roads we drive on. Of course, the total amount of available parking consists of the area where cars are parked at night, at work, and at commercial establishments. One estimate indicates that there are 2 billion parking places in the United States, collectively amounting to 26,800 km2, about the size of Vermont.
Areas covered by pavement all contribute to the footprint of humans on Earth. These areas are permanently lost to plant production and the preservation of nature. Parking lots contribute to the urban heat island effect, as no trees are present to cool the atmosphere by transpiration. A large percentage of the precipitation that falls on these areas is rapidly lost to streams and rivers, constituting what hydrologists call “quick flow,” which contributes to the likelihood of urban flooding. There is little opportunity for this runoff to interact with soils, which often remove pollutant elements, such as nitrogen, phosphorus, even arsenic.
The love affair of the human species and their cars takes a toll on nature, exacerbated by the increasing number of humans on Earth. We have made great strides in removing air pollutants from automobile exhaust and with an increasing fleet of electric vehicles, which reduces impacts on the Earth’s climate. But, we have given scant consideration to the impact of parking automobiles on the natural biosphere that sustains life on Earth.
Imhoff, M.L. et al. 2004. The consequences of urban land transformation on net primary productivity in the United States. Remote Sensing of Environment 89: 434-443.
Margolies, J. 2023. Awash in asphalt, cities rethink their parking needs. New York Times, March 7, 2023
Milesi, C., C.D. Elvidge, R.R. Nemani, and S.W. Running. 2003. Assessing the impact of urban land development on net primary productivity in the southeastern United States. Remote Sensing of Environment 86: 401-410.
Ritters, K.H. and J.D. Wickham. 2003. How far to the nearest road? Frontiers in Ecology and Environment 1: 125-129.
Van Vliet, J., D.A. Eitelberg, and P.H. Verbung. 2017. A global analysis of land take in cropland areas and production displacement from urbanization. Global Environmental Change 43: 107-115.