Rich,
Great question. I am no expert, but I have a few thoughts.
1) The main roads will be unsafe, backroads might be safer but still not optimal. I have used Google maps to create travel maps w/directions to get from the two non-home locations I am most likely to be at (two relatives homes). First you change the setting at the top to bicycle or walking, rather than by car; then you can opt to move the route off the main roads even more. The satellite image allows you to see where homes are and so I have set my routes to avoid roads with lots of houses.
2) Travel at night as much as possible.
3) I would think that for the first few days, such roads will be fairly safe (before people begin to really panic), whereas the highways might be clogged (if an EMP, possibly with people living in their cars while waiting to be saved.. or preying on other motorists).
4) Once you have the basic plan, you can use the map to see where you could opt for using train tracks and walking/hiking paths. I have a few places noted where I plan to use railroad bridges in order to avoid potential chokepoints of automobile bridges.
5) When you know where you will be going, you can look along the way for hiking trails, bike trails, and snowmobile trails (snowmobile trails will also have bridges).
6) State parks will have shelters you could stay in (lean to’s and the like), you could check their maps online as part of your preps.
7) High tension power lines – they usually have an access road running at their base. The lines are usually a bit away from homes, near the highway but usually separated by a stand of woods (because no one wants to look at power lines).
Then when you have finally set out your google travel map, and noted where you may optionally jump off and use some alternate trail…. Print It Out and place it in the wheel well of your car.
I look forward to seeing what other advice folks have.