Hi!! Parent of an '09 Dukie!! I have used the public transit from RDU over to Duke. It was cheap, easy and I got off at the Duke Hospital Center. It does not go through the campus, but there are other stops nearby.
Here is the web site if you want to check it all out--maps of routes, etc.
http://www.ridetta.org/Home/index.html
We went to Blue Devil Days when S1 was accepted and loved it!! He is a very happy Blue Devil to this day!!