The National Automotive Sampling System (NASS) Crashworthiness Data System (CDS) is a nationwide crash data collection program sponsored by the U.S. Department of Transportation. It is operated by the National Center for Statistics and Analysis (NCSA) of the National Highway Traffic Safety Administration (NHTSA). The NASS CDS provides an automated, comprehensive national traffic crash database. Data collection began in 1979 in 10 geographic sites, called Primary Sampling Units (PSU's). In 2002, three additional PSUs were added to the system so that the 2004 NASS CDS file contains data from 27 PSU's. These data are weighted to represent all police reported motor vehicle crashes occurring in the USA during the year involving passenger cars, light trucks and vans that were towed due to damage. The NASS program was re-evaluated in the mid-1980's. This re-evaluation resulted in changes, which were implemented by NHTSA in January 1988. NASS now has two major operating components: (1) the General Estimates System (GES) which collects data on a sample of police traffic crash reports; and (2) the Crashworthiness Data System (CDS) which collects additional detailed information on a sample of police reported traffic crashes.