Cities Test Permeable Pavement and Vegetation to Reduce Parking Lot Heat and Runoff

U.S. are installing alternatives to traditional asphalt parking lots to lower surface temperatures and reduce stormwater runoff. At the Hampton Roads Planning District Commission headquarters in Virginia, staff replaced a crumbling asphalt lot last year with porous concrete panels, native plants, and recycled materials.

Jill Sunderland, the commission’s senior water resources planner, said the rain infiltrates faster than it can puddle on the surface and that the lot feels cooler. The City of New Orleans requires its Department of Public Works to use permeable paving where practical.

In Indianapolis, the Newfields art museum added bioretention rain gardens to one lot and a permeable grid to another. Denver’s dePaving a Greener Denver initiative aims to reduce the city’s coverage of impervious surfaces.

Reflective surface coatings are used in Los Angeles’ Pacoima neighborhood to limit heat absorption. Sacramento requires parking lot developers to plant trees that will shade half the lot within 15 years. , and Seattle impose green area requirements for new development.

Some cities install solar panels as shade structures. Vincent Cotrone, extension educator of urban forestry at Pennsylvania State University, said dark paved surfaces can raise temperatures by as much as 20 degrees and contribute to the urban heat island effect.

Warmer neighborhoods increase air conditioning use, which in turn adds heat outdoors.

Impervious pavement prevents rainwater from soaking into the ground and can carry pollutants such as oil and heavy metals into waterways. Lattice pavers, interlocking pavers, stone beds, and brick pavers allow water to filter through while supporting grass growth.

The Hampton Roads project uses a stamped concrete border that traps sediment before it reaches the porous sections. Bioswales and rain gardens use sand, soil, and plants to filter pollutants before water reaches streams or sewers. At the Newfields museum, one lot features rain gardens and the overflow lot uses recycled plastic grid pavers.

Jonathan Wright, director of the garden at Newfields, said the permeable lot works well because the space is used only about 10 percent of the time.

Alternative materials often cost more initially. Sunderland said the Virginia project was more expensive than asphalt repaving but offers longer service life. Buzz Powell, technical director at the Asphalt Pavement Alliance, said asphalt is versatile and handles heavy traffic better than some alternatives.

Powell added that any new pavement may need repairs and that owners should evaluate life-cycle impacts. Greg Kats, founder of the Smart Surfaces Coalition, said individual city changes will not produce large effects by themselves but that understanding the scale of benefits can support wider adoption.