(http://i.imgur.com/shLCshD.png)
Cities are invariably full of dead-end streets and nonsensical infrastructure.
(http://i.imgur.com/FJMtcBv.png)
When the city grows, intercity roads on diagonals are demolished and not connected (cities with diagonals will tend towards getting a lot of roads not connected to one-another eventually). As I recall Phillip (who went missing eventually...) fixed the code that made the diagonals warped, and this has worked fine for a while, but it seems that something now makes it behave in this fashion.
I will have to look into the disconnexion bug when I rework the city generation code in the future.
Given that the city generation code remodelling may well be postponed until after the next release, I have now looked into this. I have pushed what I believe may be a fix to this problem. I should be grateful if anyone could re-test it and confirm whether it is fixed.
I have also improved the choice made by cities of their bridges at the same time.