"Interstate? How does that work?"
1. There was a fellow who was very good and heroic. God comes to him and says "Since you have been so good, I will grant you a wish." The fellow thinks for a minute and says "I would like a bridge so I can drive to Hawaii." God says "That seems a bit selfish and out of character." The fellow agrees and thinks some more. He says "I have a wish that will help all of mankind; I want to understand women." God replies "Do you want two lanes or four?"
2. The idea behind Interstate Highways comes from Eisenhower's trip across the country for the Army when he was a Major, to see how an Army convoy could travel across the country. It took way too long, especially compared to Germany's Autobahn. Since Hawaii has lots of military bases, they need to move quickly between them.
3. When I was there in the early 70's, gas rationing was an issue and the Federal Government mandated speed limits of 65 MPH. Most states had to reduce their limits anywhere from none (Nevada), 75, or 70 to 55. To comply Hawaii had to raise their maximum speed limit from 55 MPH to 65 MPH.
4. There was probably some politics involved.