[Talk-us] US Trunk road tagging

Wed May 5 15:15:51 UTC 2021

On Tue, May 4, 2021 at 11:18 PM Evin Fairchild <evindfair at gmail.com> wrote:

> 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.
>

I've taken a long look at the NHS system maps
<https://www.fhwa.dot.gov/planning/national_highway_system/nhs_maps/> for
my rural region around Vermont (VT
<https://www.fhwa.dot.gov/planning/national_highway_system/nhs_maps/vermont/vt_vermont.pdf>
, Burlington metro
<https://www.fhwa.dot.gov/planning/national_highway_system/nhs_maps/vermont/burlington_vt.pdf>
, NH
<https://www.fhwa.dot.gov/planning/national_highway_system/nhs_maps/new_hampshire/nh_newhampshire.pdf>,
NY
<https://www.fhwa.dot.gov/planning/national_highway_system/nhs_maps/new_york/ny_newyork.pdf>)
as Evin suggests and found that it really does a good job at highlighting
the most important regional connectors in a way that is much less "busy"
than *all* US highways plus major state highways. As an example, US-7 is
one of the major highways through the region, but it drops out of the NHS
just north of where it connects to I-89 (actually I-189) as the interstate
takes over the regional-connector function from there north. While not
necessarily something that must be hewed-to exactly, the NHS classification
*does* seem like a very useful guide as to which roadways really are the
most important routes in a region that might be worthy of a trunk designation
declaring them the most important non-motorway roads.I was pleased to see
that the NHS includes VT-103 and VT-9 -- state roads that *are* the major
regional connectors that are functionally and physically equivalent to US-4
and US-2 in their construction.I also like how the NHS doesn’t include US-2
where it winds through the Champlain islands
<https://www.openstreetmap.org/#map=11/44.7531/-73.2726>, but does include
the portion that connects the bridge to NY via VT-78 and US-7. It’s not a
choice I would have thought of myself, but it makes a lot of sense from a
regional-connectivity standpoint. I also appreciate how the NHS includes a
little segment of VT-131 and VT-12 near Clairmont, NH
<https://www.openstreetmap.org/#map=14/43.4042/-72.3933>. These state
routes aren’t as important for most of their length, but in this spot they
serve as regional connectors in conjunction with I-91 and NH-12.

What the NHS maps highlight to me is that importance and connectivity do
*not* always match the highway sign. This has also been my experience as a
road user. Signed US routes may wind out of the way and have segments that
aren't so important and State routes may have portions that are critical
infrastructure, but never got included in the federal system for some
variety of historic reasons.

With respect to predominantly rural regions, I would be very happy if
highway=trunk was used for the segments of roads listed in NHS and
primary/secondary for US & State routes not in NHS. I'd also be happy with
mapper discretion to include/exclude a few edge cases not reflected in NHS,
but NHS seems like a very good baseline for regional connectivity
importance.

Lastly, using high connectivity-importance for trunk on down doesn't
preclude renderers from giving a visual indication of expressway-grade
physical condition. If we can get the highway=* hierarchy actually meaning
importance, then a later feature-request on current and future renderers
could be to give more prominence to ways tagged with expressway=yes. For
example, just giving the casing an extra pixel of weight may be sufficient
to highlight expressways, regardless of their connectivity-importance.

On Tue, May 4, 2021 at 11:18 PM Evin Fairchild <evindfair at gmail.com> wrote:

> 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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