When it closed in 1995, Stapleton had six runways (two sets of three parallel runways) and five terminal concourses. The runways at Stapleton were then marked with large yellow "X"s, which indicated it was no longer legal or safe for any aircraft to land there. The IATA and ICAO airport codes of DEN and KDEN were then transferred to the new DIA, to coincide with the same changes in airline and ATC computers, to ensure that flights to Denver would land at the new DIA. The main reason the decision was made to close the airport was because the runways were too close together. This would mean air traffic controllers would have to stagger airplanes. Also, most of the runways were too short, considering the fact that the airport was at 5,333 ft above sea level. Denver International Airport runways are all 12,000 feet in length, apart from 16/34L, which stretches 16,000 feet.