Officials believe Greenbelt would need about 60 percent more parking spaces than initially projected if the city is chosen as the site of the FBI's new headquarters.
A draft Environmental Impact Statement released in 2015 estimated only 3,600 parking spaces would be needed if it were located in Greenbelt.
The final statement, which is due next month, will call for more than 6,000 parking spaces, WTOP-FM reports.
Greenbelt and Landover, Maryland, and Springfield, Virginia, are all being considered to become home to the new headquarters, which is expected to house about 11,000 employees.
It is unclear how many parking spots would be needed if either Landover or Springfield were selected instead.