Serving one of the largest metropolitan areas in the United States, the George Bush Intercontinental Airport (IAH) in Houston, Texas, is one of the 10 airports with the longest average taxi-out and taxi-in times. This paper assesses the congestion at IAH by analyzing taxi times and flight data during different hours of the day. The capacity of IAH is investigated by examining the number of departing flights on the ground. IAH is operating close to capacity most of the time. Because increasing airport capacity can mitigate congestion, this report develops a surface operation model based on analyzed results to achieve this aim. A mixed-integer programming formulation is proposed to optimize total taxi times by finding optimal taxi routes and the related schedules. The model is applied to a sample from real data.