Proposal:Emergency access & exits

`emergency=yes`	`emergency=no`	`emergency=designated`	`entrance=emergency`	`exit=emergency`

Proposal

Formalize emergency=yes/no to indicate the usability of roads/paths to emergency vehicles, as described in #emergency=yes/no.
Deprecate emergency=yes/no for hospitals in favor of emergencies=yes/no, as described in #emergencies.
To do: What about emergency=designated?
Deprecate the highly misleading entrance=emergency (which was approved to indicate emergency exits) in favor of exit=emergency.
To do: How should entrances specifically intended for emergency services be tagged?

This proposal:

formalizes two not yet formalized tags (emergency=yes & emergency=no)
deprecates the secondary meaning of emergency=yes/no for hospitals by establishing a dedicated tag (#emergencies)
deprecates the highly misleading entrance=emergency

emergency=yes indicates that customary emergency vehicles can use a road or path (tagged with highway=*).
This requires the following:
- the way must physically allow passage for customary emergency vehicles regarding their width, height and weight
- if there are any barriers along the way, they must be passable for customary emergency vehicles
emergency=no indicates that any of these requirements are not met (that is customary emergency vehicles cannot use the road or path).

Note that:

Both of these tags should only be used on a way tagged as a road or path (as per highway=*).
The specific type of road or path does not change the meaning of these tags. E.g. emergency=yes still means that emergency motor vehicles can use the way if it is tagged with highway=footway or highway=cycleway.
Neither of these tags implies anything about access=*. If the element is reserved for emergency services (i.e. may not be accessed by regular citizens), you should additionally add access=no or access=private.
Emergency services are not restricted by legal access restrictions such as access=* or vehicle=*.

emergencies^[1] is used to indicate whether a hospital (amenity=hospital or healthcare=hospital) is equipped to deal with emergencies:

↑ The key name is of course up to debate. emergency_room=* is currently used about 50 times. Given the approved emergency=emergency_ward_entrance tag emergency_ward=* would perhaps be even more consistent with the established tags. However such a tag seems to be a bit misleading since a hospital probably has multiple emergency rooms/wards, so naming the tag "emergencies" (as in does the hospital handle "emergencies"?) seems to be preferable.

Please comment on the discussion page.