The exception to maxwidth is not for a class of vehicle, but for a
"purpose", i.e. reaching a property along that road. I'm not sure of the
actual legal meaning of "access" in this case but it's probably
something like that. So "loading" would also be in this category, but
"permit_holders" would not as I think this would refer to the specific
driver, or possibly the specific vehicle.
Tagging it as maxwidth=6'6" and ignoring the qualification is IMHO a
good starting point on the grounds that routers tend to ignore all sorts
of restrictions in the initial and final bits of the route anyway. But
then we should be able to add the qualification to the tagging in some
way that the cleverer routers can make sense of. So something like
"maxwidth:destination=no" or "maxwidth:exception=destination" would both
fit the bill. I think I would prefer the second option as it seems more
versatile; the first option includes redundant information (the "no" is
redundant unless anyone can think of some other useful value which might
come here). We also gain a tagging pattern which would lend itself to
many situations.
Colin
PS: in Holland it's possible to get a permit to ignore just about
anything...I know a street which is one-way except for permit-holders.
It's not signed as such at the normal start of the road (only on the No
Entry signs at the other end), so you have no idea you can expect
oncoming traffic.
On 31/05/2012 13:27, Robert Whittaker (OSM) wrote:
On 31 May 2012 11:23, Colin Smale<[email protected]> wrote:
Maybe I am just having a "blond moment" but I can't see any way of capturing
access restrictions "except for access". Loads of country roads are
signposted as "max width 6'6" - except for access" which implies a wider
vehicle will fit (just). There are other restrictions which are sometimes
qualified in this way, like "No HGVs except for access" but when they
specify a class of vehicle then the tagging is obvious - in this case
"hgv=destination". But this can't be done simply with maxwidth (and
maxweight, maxheight).
As I can't see any direction on the wiki I thought I would let up a balloon
here to see if anyone has come up with a tagging solution for this (in my
experience) typically British phenomenon.
Where I've come across these "exceptions" to the restrictions, I've
used something like:
maxweight:exception = loading;permit_holders
The other sensible way of doing it that I can think of would be to
have a separate key for each class of user taht has the exception. So
something like
maxweight = 7.5 T
maxweight:loading = no
maxweight:permit_holders = no
The first approach better reflects the reality of the signs -- it's
not a case of multiple restrictions; it's one restriction, with a list
of exceptions. The second second approach is more flexible though, and
is more consistent with the documented maxspeed:hgv tag. However, I
think the second method is slightly ugly, in that we have to have a
"no" value to remove the original maxweight.
With either method, it would be good to document a list of simple
words to express common exceptions.
Neither approach had been particularly heavily used though, as far as
I can see from taginfo.
Robert.
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