It is logical that the bigger, heavier airplanes of today require longer, sturdier runways for landing. Airport designers considered this and more when they planned the recent 1400-foot-long extension to Runway 32L at Chicago's O'Hare Field. There were two main reasons for building the extension of 21-inch-thick concrete. The solid concrete construction will eliminate shoving failures that sometimes occur on asphaltic concrete during taxiing. And the generous thickness is also expected to accommodate increasingly heavy aircraft for a long time without needing to be overlaid.