It's a good start.
A scale would go along way to determining the size of buildings, etc. (if any) are going to be added.
I think you need more than just the major roads. Side streets and alleys would probably play a major role in traffic flow.
How do they get 'fresh food' into the protected part of the city?
Just a few things off the top of my head, hopefully they make sense cause I'm not fully awake yet.