May 14, 2001

Permeable Pavement Environmentally Friendly Option for Parking Lots

The honeycomb design of Grasspave2® is visible in this example
of permeable pavement. Spreading grass helps stabilize the
mesh structure. Photo courtesy of William Hunt.

Most of us don’t consider a parking lot a thing of beauty, but the honeycomb design of some new parking lots in eastern North Carolina is easier on the environment than standard asphalt and could be considered an attractive alternative to traditional designs. 

NC State researchers William F. Hunt III, extension specialist in urban storm water in the Department of Biological and Agricultural Engineering, and John R. Stone, associate professor in the Department of Civil Engineering, are working to discover how well these new parking lots, constructed of “permeable pavement,” are performing.  Permeable pavement is a construction material that allows storm water to drain naturally through the soil rather than becoming polluting runoff.  Runoff has the potential to contaminate soil and water with oil and other pollutants.

The construction technique involves layering materials to create a lot that is both permeable to water and sturdy enough to support heavy cars.  A geotextile fabric that keeps the gravel layer stable but allows water to pass through is spread on a base layer of gravel; then a layer of sand and a concrete or plastic lattice grid complete the pavement.  The next step is to plant a spreading variety of grass such as Bermuda to add stability and texture.  Overall, these lots cost a little more than conventional lots to construct, but the price may well be worth a bit extra to protect surrounding waters from pollutants.  In fact, according to Hunt, “The total costs could be less because permeable pavement may reduce the amount of money put into infrastructure, such as ponds and storm drains.”

For about two years the research group has been observing the permeable employee parking lot they installed for the Hannibal Building in Kinston, North Carolina.  This lot contains 26 spaces and was designed by NC State civil engineering students in spring 1999.  So far the lot has performed well; it is in good condition with no runoff contaminating the surrounding area.

In January 2001 civil engineering undergraduate students Jamey T. Westmoreland, Jason A. Houston and Eric T. Taylor selected as their senior project designing a similar parking lot at Wilmington’s Legion Stadium, which is near Greenfield Lake nature reserve.  The students created a proposal for a combination conventional and permeable lot that would enable researchers to compare the effects of the two types of pavement.  Half the lot is standard asphalt and the other half is Grasspave2®, which is a set of interlocking plastic rings patented by Invisible Structures Inc. of Aurora, Colorado.  The researchers hope to observe this lot for several years to study its performance, as they have with the Kinston lot.

If these studies indicate long-term high performance both structurally and environmentally, permeable pavement could become a common sight and one that is certainly more attractive and gentler on the environment than the miles of asphalt that currently surround us.

-- rudd --

Technical Contacts:  Dr. John R. Stone, 919/515-7732, stone@eos.ncsu.edu, William F. Hunt III, 919/515-6751, bill_hunt@ncsu.edu
Media Contact:  Linda E. Rudd, 919/515-3848, linda_rudd@ncsu.edu