hi,
I changed some things on http://wiki.openstreetmap.org/wiki/Key:access -
only to document current (best) practices.
* Transportation modes
The transportation mode hierarchy picture is replaced by a simple outline,
because the picture was not integrated in the text and too small to read
on the page itself (could both be fixed), and having to figure out how to
modify the picture complicates editing of this wiki page. The hierarchy is
however the only definition of several transportation mode categories so
quite important. IMHO the picture can be re-added but not replace the
outline.
Some transportation modes were listed in two unrelated categories. This
needlessly complicates determining the correct tags for a real-world
situation. Specifically, the meaning of access tags becomes very unclear
if they belong to unrelated categories. There was apparently a good reason
for doing this but I have not found a clear explanation. (Note that
*=agricultural is not necessarily defined by this hierarchy, only tags
like agricultural=no.)
Added a separate tag for cars, because AFAICT any routing app computing
routes for cars uses this transportation mode. If routing would be done
for 'motorcar', ways tagged as hazmat=no, for example, could not be used
because the motorcar *could* be a hazmat vehicle. Maybe the actual tag is
not needed, in which case the description can stay but the tag removed.
BTW what is a hov?
Added a tag for low performance mopeds, because in some countries they are
by law neither a bicycle nor a true moped.
Separated land (road), water, and rail based transportation because they
can be treated separately(?).
* Direction specific restrictions
I listed :backward and :forward postfixes for access keys but apparently
forgot explicit descriptions. The examples should be enough for now. Some
roads (around here at least) have complicated oneway restrictions that
cannot be modeled with oneway= and cycleway=opposite*. The postfixes allow
specifying any restriction (yes/no/destination/etc.) for any
transportation mode in either direction.
I'd like to deprecate cycleway=opposite because it is used for roads that
have neither a cyclelane nor a cycleway in that direction, so using a
cycleway tag does not make much sense.
* Evaluating access tags
In order to know the meaning of a set of access tags on a way with some
highway tag (in case of roads), it is necessary to define how access for
each transportation mode can be computed from these tags. I added a
section about this which hopefully matches current tagging practice. It
does not include time-based, height, width, or weight restrictions so it
is certainly not yet complete. Many of the values listed at the top of the
page are also missing. The idea is that this model links tagging to
routing so if it used, while currently AFAIK one needs to find out how a
router computes access and tag accordingly or accept broken routing in one
or more routing engines.
Christiaan
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