A major study estimates there to be between 105 million and 2 billion parking spaces in the U.S. These results are incorporated into their life-cycle environmental analysis of various vehicles (sedans, sports utility vehicles, and pickups). The analysis indicates that parking facilities represent 0.5% to 12% of total estimated lifecycle energy consumption and greenhouse emissions, and 24% to 81% other air pollutants, depending on vehicle type and scenario. The environmental consequences of providing the parking spaces are discussed as well as the uncertainty in allocating paved area between parking and roadways.
The original study is Mikhail Chester, Arpad Horvath and Samer Madanat (2010), "Parking Infrastructure: Energy, Emissions, And Automobile Life-Cycle Environmental Accounting," published in Environmental Research Letters, *(http://dx.doi.org/10.1088/1748-9326/5/3/034001 ), an addition to "Environmental Life-cycle Assessment of Passenger Transportation: A Detailed Methodology for Energy, Greenhouse Gas and Criteria Pollutant Inventories of Automobiles, Buses, Light Rail, Heavy Rail and Air", UC Berkeley Center for Future Urban Transport: A Volvo Center of Excellence (www.sustainable-transportation.com)
Thanks to Todd Litman