Where are safe places in Left 4 Dead 2?

Where can I find places in Left 4 Dead 2 that zombies can't reach (or just the safest places)?

For example: on the third stage of The Parish, I can stay on the fence and zombies will just stand around while our team is shooting them.

Solution 1:

The safest place, by definition is the safe room.

Other safe places are rooms with doors closed, of course until infected destroy them. And in general all places that can have only few entrances (one or two) so that they can be easily guarded by your team mates. Trucks, garages, rooms and so on.

If you are instead searching places where infected cannot reach you, they probably go under definition of maps bugs/exploits. Because for sure map designer/developers do not want to add places where you can safely stay without being reached by infected.

Solution 2:

A non-exploit technique you can use goes by various names, but the one I know is mario stomping. Basically you stand on top of something that the infected would normally have to climb to get to you, such as on top of a van. Where the infected climb up the sides, just stand on top of that "ladder", and they will keep running into you as they try to desperately climb up and will keep falling back down, never hitting you.

You'll have to do this in multiple places though, since they'll try and climb up at more than once spot. This won't do anything to protect you from special infected, though.