With car parks accounting for up to 10% of land in US cities, measures to make them more environmentally friendly are urgent
Mark Harris, guardian.co.uk 18 Nov 09;
In the 40 years since Joni Mitchell sang about paving paradise, putting up parking lots remains an American obsession. Scientists estimate that up to 10% of land in US cities is now devoted to car parks, causing environmental damage whether they are used by Humvees or hybrids.
Stormwater run-off from roads, drains and parking dumps the equivalent of more than a dozen Exxon Valdez tankers of oil directly into US rivers each year, in addition to dangerous levels of heavy metals, pesticides, bacteria and industrial pollutants. Traditional car parks also encourage sprawl, contribute to urban heat islands and offer little biodiversity.
Now the US Environmental Protection Agency (EPA) has decided that it's time to turn grey car parks green. It has begun road-testing alternative paving materials that allow water to slowly filter back into the ground rather than rush down the drain.
For the test, a 4,000 sq m asphalt car park at an EPA facility in Edison, New Jersey, is being replaced by three different types of permeable surfacing and a variety of rain gardens.
Research has already shown that gardens and swales can capture up to 90% of nitrogen and heavy metals from water, but the EPA is hoping to develop new systems that can perform even better – and deal with contaminants like leaking oil.
The shift to greener car parks has its roots in the energy crises of the 1970s, when Californian cities passed laws requiring half of all parking spaces to be shaded by trees. Although the aim was to reduce temperatures in parked cars and cut demand for air conditioning, the trees had an unexpected side-effect: improving air quality. The US Department of Agriculture says that heavily shaded car parks absorb smog-producing ozone, cut overall hydrocarbon emissions from vehicles by 2% and reduce run-off by more than 175 gallons per tree.
Some sunny car parks are even getting a 21st-century twist. Photovoltaic "solar trees" provide more shade than real trees, while simultaneously generating clean electricity. The Solar Grove at Kyocera International's headquarters in San Diego consists of 25 power-generating solar trees shading 186 parking spaces.
The panels produce over 430,000 kWh a year (see daily figures online), used to power the offices, provide lighting without light pollution and, soon, recharge plug-in electric vehicles. While the artificial trees can't soak up water or pollutants, run-off flows into swales where organic and inorganic filtration yields clean water at the drain.
Such innovations are welcome, but there's still a lot of ground to cover. A recent Purdue University survey estimated that car parks in US cities take up three times as much room as parks for people, and the EPA surface research is expected to last a full 10 years.
It doesn't look as if America is going to be pulling up parking lots and replanting paradise any time soon.
