The Automotive Collision Avoidance System field operational test (or ACAS FOT) program was led by General Motors (GM) under a cooperative agreement with the U.S. Department of Transportation. This report summarizes the activities of the entire program, with an emphasis on efforts that occurred after the last program Annual Report. The ACAS system consisted of Adaptive Cruise Control (ACC) and Forward Collision Warning (FCW) systems that were developed and integrated by GM and Delphi Corporation in preparation for the FOT conducted by the University of Michigan Transportation Research Institute. The FOT involved exposing a fleet of 11 ACAS-equipped Buick LeSabre cars to 12 months of naturalistic driving (137,000 miles of driving were accumulated). The 96 test participants were lay drivers from southeastern Michigan who drove these cars as their personal vehicles for several weeks. Data gathered included over 300 data signals, including video samples of the forward driving scene and driver's face. ACC was found to be benign from a traffic safety perspective. Both ACC and FCW reduced the occurrence of short (e.g., less than 1 sec) headways, with the ACC reductions being substantially more marked and robust across driving conditions. While incidents were found during manual driving in which the FCW may have contributed to a timely driver response to an emerging rear-end crash conflict, the frequency or magnitude of such conflicts were unaffected by FCW presence. Questionnaire, interview, and focus group data indicated that ACC was widely accepted, whereas FCW acceptance was mixed. These data have suggested numerous methods for reducing the occurrence of FCW false alarms that should lead to broader FCW customer acceptability.