The Rocky Mountains initially diverted transcontinental air traffic away from Colorado, much as railroads had earlier, leaving the state with a Denver-based spur line when Colorado Airways began flying the fifty-five-minute Denver-to-Cheyenne route in 1926. As airplane technology improved, Coloradans increasingly took to the skies, and in 1938 Continental Airlines became the state's first coast-to-coast passenger carrier. After World War II, Colorado emerged as a major aviation center, with Lowry Air Force Base, Buckley Naval Air Station, and the U.S. Air Force Academy, while air travel tied Coloradans into national affairs more closely than ever before. Denver Municipal Airport opened in 1929 on a square-mile site in northeastern Denver with four gravel runways; though praised by boosters and attacked by critics as a political reward to Mayor Benjamin Stapleton's allies, it grew into Stapleton Airport, serving six major airlines and 200,000 passengers by 1950 and ranking as the fifth-busiest airport in the world in 1986. In 1989 voters approved construction of Denver International Airport, a 34,000-acre facility supported by Front Range Airport and other satellite sites, and despite criticism, delays, and cost overruns, it opened in February 1995 as the largest airport in the world.