[HOT] Trunks in Highway Tag Africa

Fernando Trebien fernando.trebien at gmail.com
Tue Jan 26 13:02:02 UTC 2021

On Tue, Jan 26, 2021 at 7:51 AM Jean-Marc Liotier <jm at liotier.org> wrote:
> With primary currently being the top of the topological hierarchy, what
> objective criteria would differentiate it from trunk if trunk becomes
> defined as "even more important than primary" ?

As in Europe and in the Anglosphere, objective criteria probably
should vary by country as conditions are not uniform across the
continent. I mention the Anglosphere because the communities of
countries like Canada [1] and Australia [2] have developed their own
set of rules based on the more general descriptions of the English

Recently in Brazil, [3] we adopted the rule "the main paved route
between any two cities/towns with more than 200k people is trunk, the
main paved route between any two cities/towns with more than 20k
people is primary." This mainly assigns trunk to national routes and
primary to regional routes in developed areas while working around
oddities (when a regional route was built and a nearby national route
was not and the regional route currently replaces its function and the
national route will not be built soon and people use the regional
route heavily because it is the best option locally) and without
leaving large areas of the territory without a trunk network (which is
the result I would expect in Africa if the current definition in
Highway Tag Africa is applied to all places on the map in Africa). In
Brazil, the resulting network is also highly correlated to maintenance
frequency (which is strongly correlated with traffic intensity), which
is a desirable property for optimal and safe driving. Two mappers
independently assessed the resulting trunk network (if we had a third
person, it would be even better), checking each other's work to ensure
that main routes are chosen correctly and that none are missing and
that none are mistakenly included unnecessarily, then they presented
the result to the local communities, who suggested some adjustments
(mainly replacing short stretches with poor infrastructure with better
alternatives nearby). This will likely require continuous fine-tuning.
Something similar happened independently in Argentina. [4] The idea
for this was based mainly on descriptions on the wiki of other
communities and on the idea that classification should be done mainly
by importance instead of physical attributes, [5] and it also
corresponds mainly to the functional classification manual provided by
the Brazilian national infrastructure authority (which does not
publish the resulting classification). The main point is that a
divided "motorway-like" road is not necessary where traffic is not
intense, and even a 2-lane single carriageway (1 lane per direction)
may be the best road available for hundreds of kilometres in some
places and vital for the region they cross.

In Bolivia, the local community applies highway=trunk to any national
route, regardless of whether it is paved or not. You can check the
unpaved ones in this image [6] or using an Overpass query. [7] The
inclusion of unpaved ways in the trunk network was rejected in Brazil
and Argentina, which managed to pave their most important roads (with
some exceptions in the North Region of Brazil). It makes some sense
that the Bolivians want to have their highway classification this way.
Since the "problem" with these ways is described on the map using
surface=*, applications should be able to make sense of them.

In Uruguay, the government provides the classification of roads. [8]
AFAIK, none of the trunk roads there are officially restricted to
motor vehicles [9] and most are only 2-lane single carriageways (1
lane per direction). Even so, they are very safe and offer excellent
mobility. The population density is low, so traffic intensity is low,
so there is no need to build expensive roads beyond this standard,
except near the metropolitan area of Montevideo. This is similar to
the situation of the trunk roads that cross the Outback in Australia,
such as Stuart Highway. [10]

In the UK, route A537 [11] is considered one of the most dangerous,
[12] not being restricted to motor vehicles and its characteristics
[13] may be below those required for highway=trunk on Highway Tag
Africa, but it has been highway=trunk in the UK for years. So, again,
Highway Tag Africa seems to promote the high standards of some
countries that are not even adopted by some other developed countries
with abundant infrastructure.

[1] https://wiki.openstreetmap.org/wiki/Canadian_tagging_guidelines#Trunk
[2] https://wiki.openstreetmap.org/wiki/Australian_Tagging_Guidelines#Unsealed_and_4wd_Roads_.28Dirt.2C_Gravel.2C_Formed.2C_etc.29
[3] https://wiki.openstreetmap.org/wiki/Brazil/Classifica%C3%A7%C3%A3o_das_rodovias_do_Brasil
[4] https://forum.openstreetmap.org/viewtopic.php?pid=711105#p711105
[5] https://wiki.openstreetmap.org/wiki/Proposed_features/Highway_key_voting_importance
[6] https://i.imgur.com/58YMeFA.png
[7] https://overpass-turbo.eu/s/12NM
[8] https://wiki.openstreetmap.org/wiki/ES:Uruguay#Correspondencia_DNV_-_OSM
[9] https://www.montevideo.com.uy/Noticias/-Pueden-los-ciclistas-circular-por-las-rutas-nacionales-Hay-un-decreto-pero-no-se-fiscaliza-uc326377
[10] https://www.openstreetmap.org/?mlat=-23.02974&mlon=133.61183
[11] https://www.openstreetmap.org/?mlat=53.2508&mlon=-2.0108
[12] https://www.dailymail.co.uk/news/article-1290797/Britains-dangerous-road-named-A537.html
[13] https://goo.gl/maps/Ag68KgNEGd6sPdTq7

Fernando Trebien

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