I have sometimes been wondering about some similar questions and even though I didn't know what to expect when I asked, the answers that satisfied me were telling how to culturally behave regarding some risk.
Let's take my example. I wondered about safety in South Africa. We can hear a lot about how some people live in gated communities, how it is supposedly unsafe. I still did not go and could not verify by myself but the answers I got and heard let me figure the risks and learned how people behaved about it. I heard that being robbed is a risk everyone takes on a daily basis. I heard that having the house robbed may also happen.
I still do not know how often that actually happens but what I understood is that unlike in the NYC subway, you do not use your brand new iPhone holding it with the tips of your fingers and yelling to it. I am using an exaggerating example but basically I could summarize an answer for the issue as there is a risk to be robbed, it happens to almost everyone living there at some point, so the precaution would be not to carry and show off expensive stuff (jewelery, electronics) and if that happens, let's get robbed but try to make sure you are not hurt.
To extend that to all cases, I would say that this would always be a cultural answer, i.e. not necessarily backed by pure facts (but statistics are very helpful). The safety of some place is not so much measured by how many people report getting robbed, or worst raped, but how people are expected to behave. It differs between locals add tourists, these being more or less wealthy than locals.
For safety of vehicles, it is harder. For most cases, it is a matter of statistics. It is very unlikely that you die on a plane but it can happen. In western societies, if you drive everyday or so, it is likely that you will have a car accident at least once in your life, but it does not mean you will get hurt. In some other countries, the roads might be way less safe, but it is always hard to measure : do people die/get hurt every 3-5 times they use a vehicle, once in their life, ... could be a way to address it. And obviously always mention the unlikely accident, i.e. there is always a risk.
And for war zone or such place, it is also hard to measure. I guess the ideal answer would be a local describing how to behave, once again, for example by dressing appropriately, not running, respecting the people you can see in the streets. I am particularly remembering going to parts of Lebanon that were strongly not recommended by my government's foreign affairs ministry but I went with a relative that lived in Beyrouth. To be honest, it was fine. There was no war at all, but the area was considered tensed. There were UN walking patrols in the streets, sometimes some tanks near official buildings and such things. But people walked in the streets casually. I would definitely not have done that by myself, but learning how people are expected to behave made me more confident about the potential risks.
Sorry for this long post, but the summary is that a satisfying answer might be to describe the expected behavior regarding the risks:
- how to get information about risks (like TV/radio/newspapers, about potential storm, wind, snow, about ongoing fights in some town)
- how to dress (to respect the culture and not to draw attention from robbers, or from militias, or to get protected in a vehicle - a helmet on a motorbike)
- how to move around, what transportation to use (it might be considered dangerous to walk or bike in L.A. for example, just because everyone drives)
- how to carry valuables (should they be hidden/not brought)
- how to interact with people (e.g. not react violently when getting robbed to avoid getting hurt, be ready to accept corruption, ...)
All these are cultural but I believe can be answered so that anyone can follow these rules.