Here are links to pages with data on ATC staffing at U.S. airports:
…Each day, traffic counts are taken at all U.S. control towers, and fed into FAA’s ATADS (Air Traffic Activity System). The data is accessible online, at: https://aspm.faa.gov/opsnet/sys/Airport.asp. An ATADS query done on 9/25/13 requesting ‘All’ facilities produced 515 locations. The data was built into this page, sorted by airport-code.
This particular page shows the substantial decline in air traffic activity, by comparing ATADS totals for 2012 with three earlier years: 1990, 2000, and 2007. This is done for each facility. Additionally, for all airports combined, the ATADS count declined 29% from 2000 to 2012, and 20% from 2007 to 2012.
…428 Control Towers were identified by either FAA or NATCA, as threatened for complete closure or reduced hours (curtailment of the overnight shifts). Furloughs in April worked to stir a large outcry from the Public and from congressional representatives. NATCA and other unions also held rallies. New legislation was quickly passed by Congress, to include paying back FAA personnel who had been forced to furlough.
…FAA’s Annual Controller Workforce Plan (CWP) contains data indicating staffing targets and actual staffing levels at all FAA ATC facilities. The 2012 CWP was used to produce this analysis of the September 2011 ATC staffing levels. The results show that in recent years, while the number of ATC operations has substantially declined, the staffing has substantially increased. In other words, work productivity per controller has declined a great deal in recent years.