Cars move along underpass built beneath a runway of International Airport at Idlewild, N.Y. While an Air France Constellation uses the runway. The underpass, part of the main highway to the 4,900 acre airport, is a "Concrete Boat" built to withstand pressure below sea level and to sustain two taxiway bridges, each capable of sustaining 300,000 pound planes. It is said to be the first underpass of its kind in the world for simultaneous movement of planes and motor vehicles. January 10, 1949. (Pho