Areas where there is more then a one 1 lane road for evacuations. If you have ever been there, there are only 2 ways out, go north or go south for about 10 miles in either direction on a one lane road.

In the summer the population of that area grows to hundreds of thousands. That area is by far the worse area for a plant. There are no evacuations signs there because there is only 1 way in and out.