The Eisenhower Interstate system was originally designed for military aircraft. every 10 miles was supposed to have a mile long stretch without bridges and signage to allow military aircraft an emergency landing or for tactical reasons if war came to our shores.
There was an interesting video on moving the U2 (or SR71 or one of those) from the Skunk Works in California out to the testing area in Nevada(?). A freeper’s dad had worked on it.
Anyway - they had surveyors and such scope out the route and move road signs, guardrails, telephone poles, etc. to accommodate the complete plane (wings and all). It was quite the undertaking, and all done in secret. “Oh, they are improving the intersection, etc.”
What was the slope requirement? One percent grade or ? Here a flat slope would be rare.