Public Parking: Assessing Stormwater Management Opportunities

In 2011, the City of Philadelphia released the Green City, Clean Waters plan, which provides a framework to reduce combined sewer overflows into the city’s streams and rivers through the use of green stormwater infrastructure (GSI). Philadelphia’s GSI manages stormwater from the public right-of-way, city property, and private properties in a decentralized fashion, so that the positive environmental, social, and economic impacts can be spread all throughout the city while it is implemented. 

This study, commissioned by the Delaware Valley Regional Planning Commission (DVRPC) analyzed a set of parking lots owned by the City of Philadelphia, but managed by the Philadelphia Parking Authority (PPA), to help PPA and the Philadelphia Water Department (PWD) identify locations where parking supply can be reduced and/or rearranged so that green surface features can be installed, maximizing green acres achieved, while minimizing impact of such retrofit on neighborhood parking capacity. 

This study developed a “Greening Capacity Score” to determine the potential for and prioritization of greening in the identified parking lots by evaluating them for three criteria: 

Pavement Condition

Parking lots in poor condition are considered better candidates for some level of green surface expression, since needed pavement repair could be taken as an opportunity to install GSI; similarly, lots in excellent, recently paved condition are less likely to warrant near term re-investment. Lots were assigned a score based on their pavement condition, ranging from 0-1, with 0 being total pavement structure failure, and 1 being a newly paved parking lot. 


This study generated a "utilization ratio," which accounts for both efficient parking lot design and average utilization of the facility. This utilization ratio ranges from 0-1, with higher ratios indicating higher occupancy and efficient parking layout, resulting in lower opportunity for green stormwater infrastructure without eliminating supply of parking spaces currently being utilized.  

Development Pressure

A development pressure score is created by collecting nearby permit activity, establishing a control factor for the amount of development that would displace greening opportunity, and discounting the score for the car-dependence of the neighborhood surrounding the parking lot. Short of conducting a full market study, this approach helps the City consider not only which lots may be suitable for greening but also redevelopment as homes, shops, and businesses.

As a senior planner at NV5, JVM Studio's Jonas Maciunas developed capacity/utilization and development pressure scoring methodologies and created an formula that combines the three criteria to generate an overall “capacity for greening” score. He packaged the NV5's findings into an document designed for technical and non-technical readers, alike. The report includes a detailed description of scoring methodology and summary pages for each lot under consideration.