Denver has traditionally been home to one of the busier airports in the nation because of its location. Many airlines including United Airlines, Western Airlines, the old Frontier Airlines and People Express were hubbed in Denver and there was also a significant Southwest Airlines operation at the old Stapleton International Airport. At times, Denver was a hub for three or four airlines. The main reasons that justified the construction of DIA included the fact that gate space was severely limited at Stapleton, and the Stapleton runways were unable to deal efficiently with Denver's weather and wind patterns, causing nationwide travel disruption.