Illinois, Indiana, Michigan and Wisconsin have almost three spaces for every car. That means more urban heat and less runoff.
- The first regional survey of parking lots found 1,260 square kilometers of paved spaces in Great Lakes states.
- Parking lots lead to hotter cities, less ground water and less healthy streams.
- The solution of parking lot overpopulation is to change how parking is used and regulated.
The states of Illinois, Indiana, Michigan and Wisconsin together have 1,260 square kilometers of paved parking lots, according to a new study. That amounts to more than 2.5 spaces for every car and almost five percent of urban land use.
And that's not counting on-street parking and parking structures.
"Every vehicle is also associated with a home, so it's really more like three or three and a half spaces per car," said landscape ecologist Amelie Davis, who worked on the study while at Purdue University.
Ample parking spaces may seem like a good thing until you consider the negative effects of all that pavement. Previous research has shown that pavement makes cities hotter in the summer, increases run-off, decreases water reaching local aquifers and even warms up rainwater before it reaches streams -- to the detriment of aquatic wildlife.
"Anyone who walks on pavement barefoot knows," said Davis of the way asphalt turns baking hot in the sun
To quantify the parking lots in the Great Lakes states Davis and her colleagues used aerial images of various randomly chosen urban areas in the states and traced only those things that are clearly parking lots. The tracings were collected and quantified by GIS (geographic information systems) software to calculate the parking lot areas.
"Basically all we did was trace with the mouse," Davis explained, "so you have a digital layer of all the parking lots."
They then scaled it up statistically to get a estimate of the states' parking lot areas. They published the results in the May 30 issue of the journal Landscape and Urban Planning.
Just why there is so much parking is a matter that has long been of interest to Donald Shoup of UCLA.
"Parking is so heavily regulated in terms of minimum spaces," said Shoup. Typically city or county regulations require a certain minimum number of spaces per square feet of floor space of business. The type of business matters too.
Restaurants, for instance, require more space than an accountant's office. But it's a minimum, not a maximum number of spaces, and there is a tendency for businesses to lean towards more spaces, since no one wants to lose a customer because of lack of parking.
As a result, cities have no way of knowing how many parking spaces there are, Shoup said.
Several things can be done, however, to keep parking lots from taking over, he said. One is to set maximums for parking spaces. Another is to allow businesses and residential areas to share parking areas, so that a bank, for instance, uses the parking during the day and a bar uses it at night.
"It's very difficult to get permission to do it," said Shoup. "You have to go through an elaborate calculation."
Ultimately, the best answer is to reduce or eliminate minimum parking space requirements and to charge for parking, said Shoup. And the latter idea only really works if the money made goes toward improving the area where the parking is located.
"Everybody wants to park for free, including me," said Shoup. But not if it leads to more seas of pavement.