[OSM-talk] Highway=trunk : harmonization between countries ?

Greg Troxel gdt at lexort.com
Sat Aug 19 12:00:21 UTC 2017

Colin Smale <colin.smale at xs4all.nl> writes:

> Interesting approach, which might work for Europe, but at the moment I
> am not entirely convinced. What is strategic at a European level might
> not be so strategic locally, and vice versa. The European numbers are
> also not signposted everywhere, so there may be a challenge of
> verifiability. I believe the European definition basically defines the
> endpoints and a few waypoints, and it is left to national authorities to
> join the dots as they wish. So it may or may not achieve your goal of
> having a harmonised definition between countries. 

I agree with caution in trying to change anything.

"Strategic" is an imprecise term.   In the US, different people have
different opinions about which roads are important, depending on where
they live and where they want to drive.

The tagging scheme is very much the UK system, and has adapations in
other countries.  In the US, motorway/interstate is easy, and we more or
less have primary for US highways, secondary for state highways, and
tertiary for the next level of importance (reaching adjacent population

In the US, "trunk" is fairly well defined.  It's a road that is
substantially more than a regular highway in that it has some aspects of
a motorway.  To be "motorway" (interstate class), the road needs to be
divided, multiple lanes, no stoplights, no at-grade intersections, with
controlled access.  To be trunk, the road has to be part way to that
standard.  So that means that almost all trunks are divided with
multiple lanes in each direction, but they typically have some
intersections (every few miles to maybe every mile), and may have some
but not a lot of non-ramp access.  They often have narrower lanes than
Interstate specifications allow.

Around me, the poster child for trunk is Route 2.  It's the second most
important east-west road in Massachusetts,, and in many places has two
lanes each way, is divided, and has occasional farmstands and roads on
the edge, but fairly few.  Lights (and one rotary) are at least a mile
apart, and sometimes 5ish miles apart.  But, way out west, it is no
longer trunk - it's just ~Main street, undivided, one lane each way,
lights, houses.  There it's highway=primary, because it's still a key
route, as important as a US highway.  In some places it meets motorway
specs and is tagged as such.

Calling a regular highway trunk, when it should be secondary or primary
would defeat the purpose of trunk, which is to identify roads that feel
intermediate between regular US highway and Interstate.   We don't have
any formal designation between US highway and Interstate.

In addition, there's history of people wanting to retag highways to
match their own view of these tags, and many others being unhappy about
this.  This is hugely important in OSM, which is about a group of people
cooperating to improve the map.

> Are you actually sure there is a problem to be solved? Do you have
> examples of inappropriate or inconsistent use of highway=trunk? 

That's a very good question.   Certainly I find cases where roads are
over or under tagged, and as long as it's occasional, I just fix them to
match the norms of the larger surrounding area.   This is very different
from trying to make large-scale changes in what the tags mean.

Perhaps the OPs could rephrase the discussion in terms of what seems
wrong with actual tagging and how that impacts users of the database
(not any particular render :-).

All that said, a problem in OSM is the blurring of road classification
and road characteristics.  But that partially reflects a larger societal
blurring in terms of how people identify and use roads.   It partially
reflects a choice made by renderers to emphasize classification.
Imagine a map where colors depend on whether the road is divided, how
many lanes it has, and intersection frequency, and aren't affected by
government labels!
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