ForewordThe 100-Car Naturalistic Driving Study was undertaken with the goal of obtaining data on driver performance and behavior in the moments leading up to a crash. This type of data is not available from either of the traditional methods of studying driver behavior in regards to crashes and traffic safety, such as empirical studies and crash databases (e.g., General Estimates System and the Fatality Analysis Reporting System). Crash databases are derived from police accidents reports (PARs) and contain a wealth of data describing the non-controversial facts of the crash such as location, number of vehicles involved, type of crash, and time of day. For a variety of reasons, however, these databases do not provide good insight into the driver behavior and performance leading up to the crash. The empirical method provides a different approach to investigating driver behavior by studying how people drive under various conditions. These studies are usually conducted as highly controlled experiments using instrumented vehicles to obtain a variety of vehicle and driver performance data. Typically, these studies involve drivers operating study test vehicles for a short period of time (i.e., a few hours) in a contrived environment (i.e., either simulator or closed test track).Naturalistic studies can be used to understand crash causation and driver behavior and supplement information learned through epidemiological and empirical approaches. Naturalistic studies include driver/subjects operating vehicles in their daily lives (e.g., commuting to work) for an extended period of time (e.g., one year).