I'd attempt to run, but more than likely would then be killed. Let's face it, everybody on this forum, no matter how highly skilled they think they are, would more than likely die in this kind of situation, or in a city-wide outbreak in general. Survival (without a city destroying missile lol) would be pure luck, or some amazingly quick wit and strategy. When it comes to it, the average human can live 40 days without food, so if it were to happen, my first scenario would be to stay in my home, take water up into my loft and stay there, since the access to the loft is through one of those trap-doors on the roof of the hallway, and is lockable from inside.
Water and staying put in an area that zombies can't get into, you can't beat simplicity
ETA - since the only part of a zombie that is alive is part of their brain, then within those 40 days, I think it's fair to say (since their outdoors and easily accessible to insects) that the majority would either not be able to move anymore, or the rotting and being fed on by insects and the decomposition from the sun's heat would leave them fully dead or completely non-threatening.