Designers were challenged to create a slender structure that would resist both wind and seismic forces. Wind-tunnel tests were used to establish the proportions of the tower, and chamfered corners of the tower shaft were designed to reduce the “vortex shedding” action of the wind. The tower is located between two underground passenger shuttle tunnels, which required the site designers to structurally coordinate the tower’s foundation with the design of the underground tunnels on either side. When designed, the Denver International Airport control tower was the tallest control tower in North America.