[Talk-us] Maxweight in the USA

Toby Murray toby.murray at gmail.com
Mon Nov 2 22:28:32 UTC 2015

My view is that this isn't much different than speed limits. We don't
tag maxspeed=96.5606, we tag maxspeed=60 mph. Tag what's on the sign.
The complicating factor on this is of course that "ton" has at least 3
different meanings but I would generally assume that weight
restrictions in the U.S. are tagged in short tons because that's what
is on the sign.


On Mon, Nov 2, 2015 at 3:59 PM, Andy Townsend <ajt1047 at gmail.com> wrote:
> Just a heads up...
> There's a bit of a discussion going on at the moment as to whether it makes
> sense to store SI units (or actually a derivative - metric tons) in
> maxweight tags.  I noticed a few changes (initially to other values in the
> UK), and commented on https://www.openstreetmap.org/changeset/35009662 , and
> the person making a changes (who's the author of one of the popular routers
> using OSM data) wrote a diary entry here:
> https://www.openstreetmap.org/user/karussell/diary/36220 .
> The argument in favour of the change is that storing an SI derivative makes
> the data easier to consume; my counter-arguments are that (a) it makes it
> harder for mappers to verify values and (b) anything consuming data
> shouldn't assume the data is valid anyway (for "Bobby Tables" reasons if for
> no other).
> Whilst doing this I noticed that a bunch of other "x tons" weight limits had
> had values changed a while back (see for example
> http://www.openstreetmap.org/way/32719427/history ).  That's now been
> changed to "maxweight=4.5359237" which is at least not heavier than the
> actual posted restriction.  However there are still some other integer
> values without units which implies metric tons (see for example
> http://overpass-turbo.eu/s/cqw ).  It may be that Pittsburgh has woken up
> one morning and decided to adopt SI units ahead of the rest of the country,
> but I doubt it.  Logically I'd expect a router encountering "maxweight=10"
> in the USA might want to interpret it as "10 US tons" rather than 10,000 kg,
> but based on the above I suspect that at least one router isn't going to do
> that.
> The relevant wiki page http://wiki.openstreetmap.org/wiki/Key:maxweight does
> say "as of September 2014 only metric units of weight (metric tonnes or
> kilograms) are supported for this tag".  I'm unaware of any discussion prior
> to the 17 September 2014 change (not that that means that it didn't happen,
> just that I'm unaware of it).
> I'm not from the US, and I'm not sure what the right answer is (if as a
> community you're happy entering maxweight=4.5359237 it'd certainly make
> everyone's lives easier), so I'm posting this here and then retiring back
> across the Atlantic :)
> Cheers,
> Andy (SomeoneElse)
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