Yes, using the flat interstate sections as emergency airstrips is true. Remember, the military has to have a plan for everything - it DOESN'T have to make sense. The interstates drew their inspiration from the pre-WWII German autobahns, which greatly impressed General Eisenhower. He also noted that even during the fall of Berlin, when it was completely surrounded, the Germans were able to fly in and out with their Short-Takeoff and Landing (STOL) Feiseler Storch aircraft, which used one of the broad boulevards in the center of the city as a runway.