"Even I was surprised by these numbers," says Pijanowski. "I can’t help but wonder: do we need this much parking space?"
Pijanowski says that car parks are a major source of water pollution. Indeed, according to computer models, car parks in Tippecanoe County produce more than 450kg of heavy metal run-off each year. This is because heavy metals, such as from car batteries and airborne fumes, accumulate on the impermeable surface of parking spaces. These are then flushed away into rivers and lakes when it rains.
The amount of heavy metal runoff is about 1000 times that of what the same area of agricultural land would produce, says Bernard Engel, who performed the modelling study. This is because soil is better at absorbing contaminants than paved areas.
Car parks also help increase the "urban island heat effect", which can raise local temperatures by as much as 3°C, says Indiana State climatologist Dev Niyogi. "Urban areas have a higher capacity to absorb radiation from the Sun than surrounding areas, and these areas become warmer," he adds.
Pijanowski counted 355,000 car parks in Tippecanoe County, which only has a population of about 155,000. Farmers could produce 250,000 bushels of grain in the same space taken up by the car parks, he explains. Since he did not count private properties and multiple-level parking – only parking spaces at businesses, Purdue University and other public properties – Pijanowski says his calculations are a significant underestimate. He obtained his results by using digitalized aerial images of the county taken in 2005, and analysing them to count the total number of car parks and the area that they take up.
The study could be important for other areas in the US, and around the world. In general, an increasing amount of land is being paved each year to create new parking space, which is a worrying trend.
Pijanowski suggests that one solution could be for businesses to share car parks. This approach could also benefit out-of-town shopping centres, which often have car parks that are rarely filled. Planners in the US might also do well to look at how European cities – where many amenities are within walking distance – are designed.
"People can help by first realizing that our land is not unlimited and that we need to use it prudently," he states. "They can seek a lifestyle that requires less automobile use. They can express their opinions that parking lots do not have to be as large as they are, attend planning meetings and help guide others to act."
The survey was presented at a conference of land-use experts in the Netherlands earlier this year and is the first in a series aimed at assessing the impact of vehicles on land-use patterns.