Determining Utilization Rates for Retail Parking in Mercer County, New Jersey: Is Parking Oversupplied?

Abstract

This research explores whether shopping center parking lots in Mercer County, New Jersey are larger than necessary. It also assesses the financial feasibility of converting excess parking to other uses. As a densely developed state, New Jersey’s significant impervious coverage has contributed to localized flooding and pollution from stormwater runoff. Meanwhile, studies in other states indicate that parking is often oversupplied. If Mercer County’s parking lots are underutilized, the county could potentially make better use of its land by retrofitting parking lots for greater sustainability outcomes. This would provide a generalizable case for making better use of land in developed suburban areas. I gathered data on parking occupancy by conducting a stratified sample at five representative shopping centers over three months. I drove to the selected locations at specific times and counted parked vehicles on both weekdays and weekends. More than 100 samples were collected in total, confirming that these parking lots are significantly underutilized. Next, I modeled the costs and benefits of retrofitting parking lots to reduce stormwater runoff, using the largest shopping center sample location as my baseline. I evaluated the costs of removing some impervious asphalt and replacing it with either porous asphalt, bioretention basins, or public park space. I collected cost estimates for maintaining impervious asphalt, removing impervious asphalt, and installing different retrofits from various industry websites, and I modeled the costs of these options over 25 years at varying discount rates. The analysis demonstrated a significant difference between the costs of keeping the asphalt as-is, installing porous asphalt, installing bioretention basins, or installing a public park. The public park was the most cost-effective option for retrofitting approximately 10% of a 38-acre parking lot.