The area immediately under the streets has become so full that in many places, new cable runs require digging by hand to avoid severing existing cables. The city may eventually have to build concrete tunnels under the streets to hold them all, and even that might not be enough.
Personally, I think they should just drop all pretense and start laying the fiber down on the surface of the street. Oh, I know what you're thinking: "But then the fiber would be ruined the first time a car drove over it!" Well duh, that's where the hover-cars come in. Geez, do I have to think of everything? Heh heh.