An operating concept and a laboratory analysis methodology were developed and tested to examine how four-dimensional trajectory analysis methods could support higher levels of automation for separation assurance in the National Airspace System. Real-time simulations were conducted in which a human controller generated conflict resolution trajectories using an automated trial plan trajectory generation and analysis function, but only in response to conflicts detected and displayed by an automatic conflict detection function. Objective metrics were developed to compare aircraft separation characteristics and flying time efficiency under automated operations with that of today’s operations using common airspace and common traffic scenarios. Simulations were based on recorded air traffic data from the Fort Worth Air Route Traffic Control Center and were conducted using today’s and nearly two-times today’s traffic levels. The results suggest that a single controller using trajectory-based automation and data link communication of control clearances to aircraft could manage substantially more traffic than under today’s conditions, and with improved route efficiency while maintaining separation. The simulation and analysis capability provides a basis for further analysis of semi-automated, or fully automated, separation assurance concepts.