Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
The United States Interstate Highway System was not designed with airplane landings in mind. A common urban legend states that one out of every five (or ten) miles of highway must be straight and flat to allow emergency (or military) airplane landings, but this is not the case. However, several parts of the German and later the Swiss Autobahn system were indeed designed to be auxiliary military air strips, both during World War II and the Cold War. Additionally, the Swedish Air Force built landing strips into their highway system starting in the 1950s with some expansion continuing into the 1990s. Poland also contains highway strips for landing and takeoff, as do Finland, Singapore and Bulgaria. The Eyre Highway, which crosses the Nullarbor Plain in Australia, has four allocated areas for Flying Doctor aircraft to land.