[Talk-us] US Trunk road tagging

[Paul Johnson]

On Tue, May 4, 2021 at 10:18 PM Evin Fairchild <evindfair at gmail.com> wrote:

> 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 and highway=motorway_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 and intended main use." [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]

The wiki should be reflective of how things are mapped, not
prescribing how to map.  The wiki should be updated to reflect this.

> 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.

The NHS should not be a frame of reference, as there are a lot of
situations where what the state has built up and what route people
actually take simply doesn't reflect NHS's often absurd take on the
national grid.  But, if you really do want to base your routing on
that, we already have NHS routes in the map as route relations.