[Talk-us] US Trunk road tagging

[Adam Franco]

On Wed, May 5, 2021 at 5:05 PM Paul Johnson <baloo at ursamundi.org> wrote:

> > 3. Trunks should be important roads that fill in gaps in the Interstate
> system between two large cities. This can be 4 lane US highways, but it can
> also be 2 lane US highways, 4 lane state highways, you get the idea. The
> main idea is that the road is filling an important gap in the interstate
> system.
>
> That's what we have highway=primary for.
>

Using highway=primary as the highest class for 2-lane roads fails because
it loses the idea that there are very important long-distance connectors
that should be visible at low-zoom maps but don't have the traffic demand
to warrant the expense of adding bigger physical infrastructure. Compare
Carto's z6 and z7 rendering of the UK
<https://www.openstreetmap.org/#map=7/54.553/-2.626> and the US midwest
<https://www.openstreetmap.org/#map=7/37.423/-94.713> and note the
difference in connectivity. A lot of the smaller roads through the far
reaches of Scotland, Wales, and even England are non-motorway 2-lane roads
that are physically constructed like many of our US highways and state
highways.

As an example, the A828
<https://www.openstreetmap.org/way/29551321#map=11/56.5406/-5.2782> from
Oban to Glencoe Scotland is a small 2-lane coast-road without a shoulder
<https://www.mapillary.com/app/?lat=56.53804316&lng=-5.30388315&z=17.402428472937416&pKey=dS7J0mziCXvRUlKQdI8heg&focus=photo>
for much of its length. It is however, the only connector road between the
regionally important towns and cities of the west coast of Scotland. I get
that OSM is based on the British classification system directly so it can
be hard to retrofit actual principals onto British mapping practice. That
said, I think we can avoid many of our problems by using 'trunk' as "the
most important non-motorway roads" and not jumping right to primary. By
jumping right to primary we lose the ability to filter data at low zooms to
show only the most important long-distance and regional connectors and end
up with this low-zoom patchwork of motorway islands that is hard to make
sense of.

At this point I'm thinking of the
highway=trunk,primary,secondary,tertiary,unclassified,residential values as
simply funny labels for descending numerical values of
connectivity-importance. I'm now on board with the position that only
motorway implies any physical characteristics.
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