NASS CDS has detailed data on a representative, random sample of thousands of minor, serious, and fatal crashes. Field research teams located at Primary Sampling Units (PSU's) across the country study about 5,000 crashes a year involving passenger cars, light trucks, vans, and utility vehicles. Trained crash investigators obtain data from crash sites, studying evidence such as skid marks, fluid spills, broken glass, and bent guard rails. They locate the vehicles involved, photograph them, measure the crash damage, and identify interior locations that were struck by the occupants. These researchers follow up on their on-site investigations by interviewing crash victims and reviewing medical records to determine the nature and severity of injuries.

Interviews with people in the crash are conducted with discretion and confidentiality. The research teams are interested only in information that will help them understand the nature and consequences of the crashes. Personal information about individuals - names, addresses, license and registration numbers, and even specific crash locations - are not included in any public NASS files.

The data collected by the PSU's are quality controlled by one of 2 NASS Zone Centers.Each Zone Center, staffed by the most experienced crash researchers, is responsible for half of the PSU field offices. Zone Centers have the responsibility for coordinating and supervising the activities of the field offices, keeping field offices informed regarding changes in functional and administrative procedures, sharing ideas and concepts throughout the system regarding new techniques, procedures, and components found on vehicles and updating field offices regarding changes in system hardware and software.

NASS case review is conducted at the Zone Center and may result in case data being sent back and forth between the Zone Center and the PSU several times until the case passes quality control standards built into the NASS data collection cycle. Once data is approved for inclusion into the NASS database, it will again be subjected to quality assurance checks before becoming publicly released as part of annual NASS data files.

The data collected by the CDS research teams become permanent NASS records. This information is used by NHTSA for a variety of purposes, including:

• Assessment of the overall state of traffic safety, and identification of existing and potential traffic safety problems.
• Obtaining detailed data on the crash performance of passenger cars, light trucks, vans, and utility vehicles.
• Evaluation of vehicle safety systems and designs.
• Increasing knowledge about the nature of crash injuries, as well as the relationship between the type and seriousness of a crash and the resultant injuries.
• Assessment of the effectiveness of motor vehicle and traffic safety program standards. Evaluation of alcohol and safety belt use programs.
• Evaluation of the effect of societal changes, such as increased traffic flow and increased large truck traffic.