This study outlines a method to evaluate runway layouts using simulation, to aid in the airport planning and decision making process. As a sample study, the maximum throughput capacities of proposed expansion alternatives at Philadelphia International Airport (PHL), constrained at varying levels, are identified. The objective is to compare these ultimate airport capacities achievable for each of the different layouts to estimate their respective efficiencies in terms of runway system utilization. TAAM (Total Airspace and Airport Modeller) is used to simulate each proposed alternative given its capabilities for modeling at a very high level of detail and closely representing reality in terms of applicable separation standards and air traffic control procedures.