I am working on something similar with the prospect of getting CannonJS physics to work so that one can walk the city (in my case procedurally generated): https://twitter.com/dirkk/status/309024330115842049

I also tried a multi-device approach for visualisation: http://www.youtube.com/watch?v=-TiZzovx5YE

Any chance of collaboration?

From this thread I reckon there are quite a few people working on something similar. I guess it would be extremely cool if we could join forces.