In many survival scenarios, the term "shelter in place" is used....in other words, stay where you are until rescue arrives! Unfortunately under many "worst case scenarios", there will be no rescue! Remember Hurricane Katrina? Many died because they "sheltered in place" & were woefully unprepared for what happened! Don't count on FEMA to rescue you!
As the above 2010 Census graphic shows, while many states are heavily urbanized, most states have rural areas! State Parks, National & State forests belong to everyone...you won't be trespassing!
Urban areas with normal crime, will go ballistic when the SHTF...there are not enough police or firemen to cover any large urban area...another Katrina example. Many of these First Responders have their own families...many may not even show up! Hey, it's human nature!
Realize these extreme scenarios...after an EMP for example...no electricity, cars & public transportation will be useless, even backup generators will be fried. Depending on time of day, roads will be blocked, Interstates clogged and useless. Obviously the time to leave the urban area is before the bad stuff happens.
Let me give an example of "pre-planning". In Michigan, it seems every Tom, Dick, & Harry has an up-north "Hunting Camp" in the woods. Often multiple families will go together to buy 400-500 acres. These camps will make an excellent rural survival compound and many are just for that purpose! Just get to your refuge first, before the SHTF!
#Preppers will always talk about planning, that's what we do. Plan your "escape" from a urban environment, have backup plans, various routes, destinations! Don't be caught in the urban jungle!