What was the slope requirement? One percent grade or ? Here a flat slope would be rare.
Congress passed the Federal-Aid Highway Act of 1956 creating federal funds for interstate highway construction. As the IHS developed so did its ability to support national defense. For example, throughout the system, mile-long stretches of concrete pavement double as emergency landing strips for military aircraft. Many Army posts, especially where division-level units are garrisoned, are near interstate highways.
For example, the 1st Infantry Division at Fort Riley, Kansas, is adjacent to I-70, and the 1st Armored Division at Fort Bliss, Texas, is close to I-10.
When I worked for a major airline and took part in cargo design of the 777 Boeing engineers also discussed the ability to land on an interstate. Thats as good as I know. I will try to look at the commission report for congress, but it will have to wait another day...