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additional runways would provide some relief during poor weather conditions. The construction of a parallel runway provides the best capacity increase to an airfield system. This process, however, is a very costly and a potentially time consuming measure. Furthermore, TxDOT will require that the project be justified in order to receive funding assistance. For planning purposes, however, consideration will be given to the construction of a parallel runway for the ultimate planning period. Analysis in the next chapter will determine if the construction of a parallel runway is feasible. RUN\VAY ORIENTATION The airport is served by four runways. Primary Runway 12-30 is oriented in an northwest-southeast direction; Runway 8-26 is oriented east-west; Runway 4-22 is oriented southwest-northeast; and Runway 17-35 is oriented north-south. For the operational safety and efficiency of an airport, it is desirable for the primary runway of an airport's runway system to be oriented as close as possible to the direction of the prevailing wind. This reduces the impact of wind components perpendicular to the direction of travel of an aircraft that is landing or taking off (defined as a crosswind). FAA design standards specify that additional runway configurations are needed when the primary runway configuration provides less than 95 percent wind coverage at specific crosswind components. The 95 percent wind coverage is computed on the basis of crosswinds not exceeding 10.5 knots for small aircraft weighing less than 12,500 pounds and from 13 to 20 knots for aircraft weighing over 12,500 pounds. Wind data specific to the San Marcos Municipal Airport is not available. Thus, weather data for the nearby Austin area between 1988 and 1997 was collected to determine wind coverage for the airport. This data is graphically depicted on the wind rose on Exhibit 3A. As depicted on the exhibit, only Runway 17 -35 provides over 95 percent wind coverage for all crosswind components. Primary Runway 12-30 provides nearly 95 percent coverage, at 93.18 percent for 10.5 knot crosswinds and exceeds 95 percent for higher components. Crosswind Runway 4-22 provides 88.81 percent and Runway 8-26 provides 84.86 percent for 10.5 knot crosswinds. The coverages indicate that winds are predominantly from the north/ northwest or south/southeast. Combined coverage of all four runways is 100 percent for all crosswind components. As discussed in the first chapter, San Marcos was originally constructed and utilized by the United States armed forces as a training facility during World War II. Similar facilities were constructed throughout the country, especially in the South and Southwest. Construction of these facilities typically followed a "cookie cutter" approach where three or four runways were built to accommodate nearly all wind conditions. 3-3