[Talk-us] US Trunk road tagging

[Evin Fairchild]

Hello,

So there was a previous thread on this mailing list earlier today that
started out as just a discussion on some changes that were made to some
highway classifications in part of Colorado, and then morphed into a
discussion regarding trunk road tagging in the US. Since we ended up going
off on a tangent, I'm starting a new email thread for this discussion.

Anyway, it seems like many of us who replied to that email chain (myself
included) don't agree with the current tagging convention in this country
of tagging only divided highways (aka "expressways") as trunk. Not only
does this lead to routes frequently switching from trunk to primary when a
road becomes divided or undivided, (resulting in a particular route looking
all broken up at low zooms that show trunk roads but not primary roads) but
it also goes against what it says on the wiki: "Only highway=motorway
<https://wiki.openstreetmap.org/wiki/Tag:highway%3Dmotorway> and highway=
motorway_link
<https://wiki.openstreetmap.org/wiki/Tag:highway%3Dmotorway_link> indicate
quality. Other road types, from trunk to tertiary to residential, service,
path, footway, cycleway or track, do not imply anything about road quality,
only importance
<https://wiki.openstreetmap.org/wiki/Proposed_features/Highway_key_voting_importance>
 and intended main use
<https://wiki.openstreetmap.org/wiki/Tag:highway%3Dpath>." [1]

Given what is stated on the wiki, it seems that our way of tagging trunk
roads goes against the consensus of the wider OSM community regarding
importance being the way to tag roads. (per this discussion on the wiki:
[2]) Also it was pointed out that there is a expressway=yes tag that should
be used to denote divided highways/expressways.[3]

In that previous email chain, I proposed using the National Highway System
to denote which roads should be trunk. According to the FHWA's website, "The
National Highway System (NHS) includes the Interstate Highway System as
well as other roads important to the nation's economy, defense, and
mobility. The NHS was developed by the Department of Transportation (DOT)
in cooperation with the states, local officials, and metropolitan planning
organizations (MPOs)." I would encourage everyone to check out the maps of
NHS routes to see if they make sense for your state. [4] One comment I must
make about this network is that it includes urban principal arterials as a
part of this network. I would not make any of those be trunk, since that
would mean that there would be way too many trunk roads in an urban area.
Personally, I don't think roads that are part of the NHS should be tagged
as trunk unless they're part of a state or US highway.

Other people have suggested just tagging all US routes as trunk, but I
don't necessarily agree with that because some US routes aren't as
important as others, particularly when they parallel an Interstate. Also
there might be some important state routes that could be worthy of being
tagged as trunk, particularly if they have sections that are four lanes and
divided, or connect small/medium cities (between 100-500K metro population)
to each other.  However, if some people feel that the NHS is a bit overkill
for use as a standard for tagging roads as trunk, then I'm okay with just
tagging US routes as trunk.

Whether or not we go with the NHS or just the US highway network for
determining which roads are tagged as trunk, I'm personally okay with
allowing any divided highway/expressway to be tagged as trunk, regardless
of whether or not it's a US highway or part of the NHS. I understand that
there are some who are pretty dead set on having trunk roads be divided
highways/expressways.

I think it was clear from the previous email chain that there was a feeling
that some people aren't happy with the way we currently tag trunk roads in
the US. I really would like to come to an agreement on a better way to tag
trunks here in the US, so we don't keep having these discussions over and
over and over again. What do you all think about this? Should we use the
NHS to determine which roads should be trunk, or should it just be US
highways? Would love to hear everyone's thoughts on this. Also, I wasn't
sure if I should send this out to the tagging mailing list as well (I'm not
on that list right now), but if someone thinks that their input would be
valuable, feel free to add them to this email chain.

Thanks, Evin Fairchild (aka compdude)

[1]: https://wiki.openstreetmap.org/wiki/Key:highway#Assumptions
[2]:
https://wiki.openstreetmap.org/wiki/Proposed_features/Highway_key_voting_importance
[2]: https://wiki.openstreetmap.org/wiki/Key:expressway
[3]: https://www.fhwa.dot.gov/planning/national_highway_system/nhs_maps/
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