For years, researchers have dreamed of improving air traffic safety and efficiency by giving pilots a real-time 3-D display that shows how to navigate terrain, even in bad weather. But merging Global Positioning System data with graphical displays of the earth’s surface proved dauntingly expensive. As a PhD candidate in aeronautical engineering at Stanford University, Andrew Barrows delivered the first practical, inexpensive “highway in the sky. ”He did it by writing software that merges GPS location information with images from terrain databases and shows the pilot a series of rectangles. The pilot need only keep the plane flying through these targets. “Fifteen years from now, every airplane will have a sophisticated version of this, ”says John Hansman, MIT professor of aeronautics and astronautics. While the Federal Aviation Administration works on certifying this type of system, Barrows has left academe to become president of Nav3D in Palo Alto, CA.One big client, Boeing, is adapting his technology for military use.Nav3D is also exploring displays that would help construction crews “see” underground gas lines or guide firefighters through smoky buildings.