[OSM-talk] Highway=trunk : harmonization between countries ?
fernando.trebien at gmail.com
Thu Feb 15 18:14:42 UTC 2018
Landing on this discussion several months late. I've just heard of it
by reading a wiki talk page .
Since 13 February 2009, the wiki  criticises highway classification
as problematic/unverifiable. This has also been subject to a lot of
controversy (and edit wars) in my local community (Brazil), especially
regarding the effect of (lack of) pavement.
In trying to achieve greater consensus some years ago, I decided to
seek opinions elsewhere and finally I arrived at this scheme  which
I think is very useful, if not perfect yet. It can be easily
summarised like this:
- trunk: best routes between large/important cities
- primary: best routes between cities and above
- secondary: best routes between towns/suburbs and above
- tertiary: best routes between villages/neighbourhoods and above
- unclassified: best routes between other place=* and above
For example, the best route between two villages would be at least
tertiary. So would be the best route between a village and a town or a
city. Parts of this route might have a higher class in case they are
part of a route between more important places.
It surely raises the problem of determining optimal routes. Maybe a
sensible criterion would be average travel time without traffic
congestion. A number of vehicles may be selected for this average -
could be motorcycle+car+bus+truck, or simply car+truck.
Early results in my area [4, in Portuguese] seem promising and have
produced more consensus than any previous proposals. To me, this
method seems to:
- resist alternations in classification along the same road
- work across borders (where classification discontinuities are
expected because each country is using different classification
- account for road network topology
- work in countries with mostly precarious/unpaved roads or
without/unknown official highway classes
- work between settlements as well as within settlements
Borderline cases are probably inescapable in any system that does not
use solely criteria that are directly verifiable - from the ground, or
from the law. Maybe, in certain developed countries, the system is so
well organized that merely checking signs/laws is sufficient. That
does not mean it is like that everywhere on the planet.
OSM has so far received a lot of input from communities in developed
countries (mostly Europe, North America and Australia) and hasn't
given much attention to less developed/organized countries. What comes
closest to this is what the HOT Team does, but the judgment of road
classification one can do from satellite images in a foreign country
is much more limited than the criteria that have been raised in this
thread so far.
I wouldn't endorse tags such as maxspeed:practical due to lack of
verifiability (it should be obvious that different types of vehicles
would achieve different practical speeds). It is better to use the
legal speed in maxspeed=* and describe the practical reason for a
lower speed using surface=*, smoothness=*, and, who knows, maybe the
not yet approved hazard=*  (though that is intended for signed
hazards, not subjective/opinionated hazards).
For the sake of long-term sanity, I also wouldn't mix the purpose of
one tag with the purpose of other tags. To describe the surface, there
is surface=*, smoothness=* and tracktype=*. To describe access rights,
there is access=*, foot=*, bicycle=*, motor_vehicle=*, etc. To
describe legal speed, maxspeed=*. To describe curves, there's
Purpose, perhaps, is the main issue. What is the purpose of highway
classification? Is it to save us the work of adding extra tags? Is it
to allow the renderer to produce a cleaner output at low zoom levels?
Is it to allow routers to assume default speeds? Maybe to guide their
routing heuristics? Is it to express some sort of importance? If so,
by which perspective - urbanistic, traffic engineering, movement,
commercial value, cultural/fame, historic, some combination of those?
Should the purpose be the same in every country?
It may be interesting to also discuss the classification adopted by
other maps. I don't have a reference for Google (originally TeleAtlas)
or Here.com (originally Navteq), but Waze publishes its per-country
road classification criteria in its wiki. [6-16]
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"Nullius in verba."
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