They're supposed to be in Philadelphia, running west to escape the problem.  Problem is that they're actually in Pittsburgh in the heart of zombie country. The police dock location is still there but the docks themselves, sadly, are not.  The only thing that remains are a few steps leading down to the docks that once were.  The area where the helicopter landed is now fenced off and what I believe to be the shack that Flyboy goes into, is behind that fence.  The dark pictures of the US Steel building that you see the lights going out in when the chopper takes off.  I will get better pictures on my next trip.  But until then, please enjoy.