[Talk-us] Trunk

Greg Troxel gdt at lexort.com
Fri Oct 13 23:30:55 UTC 2017

Martijn van Exel <m at rtijn.org> writes:

> In the mean time, I decided to test some of the ideas posted here on a real
> case: The part of Michigan SR 10 northwest of the I-696 interchange:
> https://www.openstreetmap.org/relation/252973#map=13/42.5132/-83.3168
> Since 1) this road does not seem to serve an important connecting role in
> the long distance road network 2) the density of abutters and related
> driveway / parking exits I judged a downgrade warranted. Please discuss
> here or on https://www.openstreetmap.org/changeset/52903464 .

If there are enough abutters and driveways (and use of them) that people
driving on the road cannot basically act as if there are none, then it
fails as trunk, so from your description, that sounds good.

I don't think "important connecting role in the long distance road
network" should have anything to do with it.   A regular US highway that
is not divided, grade-separated, mostly limited access is still a key
interconnecting road, and it's squarely "primary".  Most of US 20 is
like this, as I understand it, and all or almost all of the parts I've
driven on (MA, WY) are like that.

> On the topic of tagging for the renderer, two things: 1) A US-specific
> rendering would be really neat 2) Trunk 'appendices' like the one I
> just downgraded do make rendering at low zooms tricky -- you end up
> with short segments that seem to end in nothing.

On point 2: Because the evolved rough consensus is about trunk being
something that would have qualified for primary that also has superior
physical characteristics, there is no reason to expect that displaying
trunk but not primary will result in a connected network or a coherent
map.  Displaying motorway but not trunk will likewise not be connected;
e.g. parts of MA 2 are trunk and part are motorway (and in Boston and
Western MA, merely primary).  The signed route is continuous and part of
the network, but if you start at Alewife you are on motorway (4 lanes
and traffic moves at 80+ mph) and eventually you get to Erving where
it's 1 lane each way, double yellow line, and posted 30, having dropped
to trunk and then had another motorway section.  But it is certainly a long
distance important route, and if you only render 2 EW routes in MA, it's
the second one to show after I-90.

My point then, is that choosing to render trunk but not primary is not
really a thing to do what preserves a sense of networks.  We absolutely
should not thing about how to use motorway/trunk/primary to make maps
rendered that way look good.

People may want to render based on ref tag, or some other "how important
is this route" tag, which could be some combination of how long the road
is and how far away the next road that goes roughly those places but is
faster is.  Others have talked about dropping some Interstate sections
(esp odd 3 digits) at small scales.

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