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2 FCW = forward crash warning. Figure ES.1. Data processing flow. Findings According to data reduction results, most crashes or near crashes are caused by driver inatten- tion and errors. These events might be prevented if appropriate instrumentation were installed to warn drivers in a timely manner. The following factors imply that the proposed systems can resolve driver inattention and errors and thus prevent a collision: 1. In the Road Departure Crash Warning System (RDCWS) Field Operational Test (FOT), the largest contributing factor to freeway crashes and near crashes was decision errors, including driving too fast or too slowly, following too closely, and misjudging a gap; more than 85% of the events were caused by this driver-related factor. For events that occurred on arterials, the same pattern followed. The next largest category for both road types was recognition errors, including inattention, inadequate surveillance, and other types of distraction; more than 5% of events were ascribed to this category. 2. In the 100-Car Study, the largest contributing factor category for crashes was driver recogni- tion errors, totaling 32% of the events. The second largest category was decision errors, count- ing 28% of the total. The largest and second largest contributing factor categories for near crashes were decision errors and recognition errors at 29% and 26%, respectively. 3. In the Drowsy Driver Warning System (DDWS) FOT, a different pattern was exhibited. The most frequent critical reason for crashes was an object in the roadway, which constituted 57% of the events. The next largest groups were the driver-related factors of recognition errors and performance errors; each had more than 14% of the cases related to driver factors. In tire strike cases, the majority were attributed to environment-related factors; more than 64% of the events were ascribed to this category. For near crashes, recognition errors and decision errors constituted 31% and 18%, respectively. 4. In the Naturalistic Truck Driving Study (NTDS), the most frequent critical factor for crashes was an object in the roadway, followed by the driver-related factors of recognition errors, deci- sion errors, and performance errors; each constituted 20% of the total cases. Not surprisingly, almost all (75%) the tire strikes involved some type of improper turn. The second and third largest categories of contributing factor for crashes were driver performance errors and deci- sion errors, respectively. For near crashes, the most frequent factor was driver-related recog-