phian efforts to implement innovative transportation policies and practices by taking a complete streets approach, increasing the availability of walking and bicycling trails and improving public transit.

Similarly, several innovative initiatives have converted vacant lots in the city to parks and other green spaces, which have been shown to improve the health and safety of those nearby (Branas, 2012). For example, a program was developed to remove trash and debris from vacant lots, grade the land, plant grass and trees to create parklike settings, and install low wooden post-and-rail fences. During the fourth committee meeting held in June 2012, Charles Branas, University of Pennsylvania, reported that these greening efforts had positive, significant impacts on several health outcomes: Gun assaults were reduced in all city sections; vandalism dropped in West Philadelphia; high stress decreased among residents in North Philadelphia; and exercise increased among residents of West Philadelphia.

The Clean Water Act of 1972 prescribes that local governments capture and treat wastewater before discharging it in rivers. Most cities treat sewage and runoff separately; however, portions of many older cities, such as Philadelphia, collect both sewage and runoff in the same system. When the combined volume exceeds the capacity of the sanitary system, the excess is discarded into the nearby river—discharges that must be minimized under the Clean Water Act. This problem, Combined Sewer Overflow (CSO), has been exacerbated by urban build-out; as more green space is paved, there is more runoff. The U.S. Environmental Protection Agency (EPA) requires cities to address CSO, in most cases by expanding their sanitary sewer or via separate piping and treatment systems. The CSO infrastructure is expensive, and there are ongoing costs.

Philadelphia took the novel approach of reusing or managing rainwater in order to prevent runoff. The alternative to CSO, called “Green Stormwater Infrastructure” (GSI), allows stormwater to percolate through the soil wherever possible, using devices such as tree trenches, wetlands, planters, green roofs, pervious paving, or rain gardens (Figure 3-1). Rain barrels promote recovery and recycling of water.

The linkages between the GSI and other systems—and the benefits that result—are not obvious, but they are remarkable (PWD, 2011):

Saving energy while mitigating and offsetting climate change. Trees and plants are an important part of the GSI, shading and insulating buildings from wide temperature swings and decreasing the energy needed for heating and cooling. Because rain is managed where it falls in systems of soil and plants, energy is not needed for traditional systems to store, pump, and treat it. Growing trees also act as carbon “sinks,” absorbing carbon dioxide from the air and incorporating it into their branches and trunks.

Restoring ecosystems. Allowing rain to soak into the ground and return slowly to streams restores a water cycle similar to that of a natural watershed. Soil is a natural water filter, and this percolation limits erosion of stream



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement