There are two folders, one for national and one for Puerto Rico. 
In each folder, there are two zip files, one for SAS format and one for CSV format.

Starting from 2014, Pedestrian and Bicyclist file is included in the file release.
Auxiliary files are included in the SAS and CSV sets instead of as independent zip files.
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FARS Auxiliary Files
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The FARS Auxiliary files are datasets that are derived from the standard FARS datasets: 
1. Accident -> Acc_Aux
2. Vehicle -> Veh_Aux
3. Person -> Per_Aux
These files are joined by the standard key variables.
Please read the following document for additional details: http://www-nrd.nhtsa.dot.gov/Pubs/811364.pdf
For User Manuals, please go to: ftp://ftp.nhtsa.dot.gov/FARS/FARS-Doc/FARS_Auxiliary_Analytical_User_Manuals.zip
For SAS Format Catalog, please go to: ftp://ftp.nhtsa.dot.gov/FARS/Auxiliary_FARS_Files_Formats

Updates
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3/24/2016:The changes are made for cases in Missouri and South Carolina.
5/18/2016: Alcohol related files are regenerated.
9/22/2017: Derived Indian Reservation data elements have been added to the Accident level auxiliary file – ACC_AUX.*. 
	The first data year of availability for the following new Indian Reservation related data elements is 2001:
	BIA – 1 indicates that the crash occurred on Tribal lands. The geographic location data collected in FARS was used in conjunction with spatial data on the Bureau of Indian Affairs (BIA) land boundaries to identify Tribal lands.
	SPJ_INDIAN – derived from FARS special jurisdiction (SP_JUR=3) element. 1 indicates that the crash occurred on an Indian Reservation.
	*INDIAN_RES – 1 indicates either BIA=1 or SPJ_INDIAN=1. This provides a more accurate representation of fatal crashes occurring on Tribal lands.
	*Use the INDIAN_RES data element to obtain the most complete data.

	ACC_AUX.* datasets can be merged with other FARS datasets by ST_CASE to obtain additional information on the crash.

8/14/2020:  The National accident.csv file has been updated for the variable "Longitute" precision from 4-digit to 8-digits.