A group of Cornell researchers teamed up to simulate what would really happen during a hypothetical zombie outbreak. Spoiler: New York City would be toast. Starting in a big city like New York or Atlanta would mean you are done from the start if the epidemic had already hit there, according to Alex Alemi, a graduate student at Cornell University and part of the research team. You are much better off starting further away from people, they say, which gives you a better chance of avoiding infection. Ideally, you'd escape to an almost empty region like the Rocky Mountains.
(Common sense points to this conclusion; I could have saved them a lot of money and time.)
Alemi and colleagues used standard disease models to estimate the zombie infection rate around the US, assuming that humans would need to be infected by a zombie bite (of course). Also following standard protocol, zombies travel only by walking and wouldn't die naturally but would need to be "killed," presumably with a well-placed blow to the head. Essentially, they used a realistic model that's very similar to the way epidemiologists calculate the spread of other viruses, but using fictional parameters unique to zombies. They did make some assumptions, including a transportation infrastructure collapse. It's hard to imagine airports staying operational for long in such a scenario. If a large percentage of the population flooded any area, the risk of infection there would skyrocket.
The video above shows how a national outbreak would play out. The top right map, susceptible humans, shows the human population that's still able to be infected. In the green bottom right map, the "killed" zombie population grows, but as you can see in the red bottom left map, so does the infected population. The top left is a composite map of the other three.
In reality, an outbreak probably wouldn't start all over the country and there are some variables. The undead might be more or less aggressive or more or less mobile. So the research team built an interactive model that allows you to simulate an outbreak, picking a starting point, a zombie-bite to zombie-kill ratio, and whether the zombies are fast or slow. The interactive model is here.