The Detailed Policy Assessment Tool (DPAT) is a widely used simulation of air traffic control that incorporates advanced technology for user-friendly operation. DPAT computes congestion-related air traffic delays, throughputs, traffic densities, and arrival/departure schedules while incorporating ground delay and ground stop programs, intrail restrictions, historical, current, or future traffic demand, a fixed or free-flight route structure, and other relevant parameters. DPAT's advanced capabilities include parallel discrete-event simulation technology and easy access through Web-based simulation.