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Surface Traffic Limitations Enhancement (STLE) is a NASA-developed advanced modeling capability for simulating airport surface aircraft movement. STLE augments NASApsilas Advanced Concept Evaluations System (ACES), which is a fast-time computer simulation of nationwide airport and airspace traffic operations. STLE expands ACES software logic and data inputs and outputs to simulate individual aircraft surface trajectories through an airportpsilas terminal gate/ramp, taxiway and runway system. STLE models surface operations using a link-node modeling structure. The modeling simulates aircraft motion dynamics, tracks the movement of each flight, assesses the traffic situation, determines route assignment, detects and resolves potential conflicts, considers node required/planned crossing time constraints, and evaluates traffic throughput and delay. Inputs include specification of link and node graph components, gate and runway configurations, operating rules and procedures, and traffic and airport operating conditions schedules, typically for a 24-hour study period. Output statistics describe transit time and delay by flight and traffic loading as well as queues and transit times by link and node. Node transit control governs actual movement of each aircraft from a link into a node and movement from a node into a link, which determines delay propagation through the surface network. STLE distinguishes sequencing nodes (e.g., taxiway intersections) and complex nodes (e.g., gate, gate group) functions. Link transit control supports this nodal network analysis process by managing traffic movement along each link to deliver aircraft to a node. STLE provides a system of working pluggable modules that represent current operations. These pluggable modules are the foundation for subsequent replacement and supplemental models.