[Tagging] Road hierarchy

[Paul Allen]

On Wed, 7 Aug 2019 at 04:40, Michael Tsang <miklcct at gmail.com> wrote:

>
> The ability of through traffic passing a road does not depend on the
> classification. As long as it is the shortest / widest / fastest path
> connecting major roads, it will have through traffic even the driving
> experience
> is the same as driving into a cul-de-sac in a neighbourhood. Therefore we
> don't need to distinguish them in the tagging. The residential /
> unclassified
> difference should be reflected in the driving experience (you expect
> houses and
> residents on residential road which you should be careful not to disturb
> them,
> but not on an unclassified road).
>

I can see your argument, but I disagree with it.  Perhaps it best describes
the situation
in Hong Kong, although I suspect not.  I definitely disagree with it when
applied to the UK.

The UK has four official, government-assigned classifications of through
roads: primary
(A roads), secondary (B roads), tertiary (C roads) and quaternary (U roads,
where U
unfortunately stands for "unclassified" which some mappers misinterpret as
meaning "uncategorized").  There are also motorways (level 0 in the 1-4
hierarchy)
and trunk roads (level 0.5 in the 1-4 hierarchy).

Standard carto gives secondary, and higher, roads their own colours and
renders
tertiary roads wider than residential roads.  This allows people to use
that most
primitive of routeing algorithms called "looking at the map."  Your scheme
would
break this whenever such a road passes through a town.  In my part of the
world
there are many "ribbon" villages along primary and secondary roads.  Perhaps
no more than a dozen houses, possibly only one one side of the road.  By
your
logic the road ceases to be a primary road and becomes a residential road.
A long stretch of red/pink road with a bleached bit where the village is.

Here, for example, is the junction of a secondary road (the B4548 which
consists of
Gwbert Road and Aberystwyth Road) with a tertiary road (North Road).
https://www.openstreetmap.org/?mlat=52.0871&mlon=-4.6543#map=16/52.0871/-4.6543
And here is an image of that junction: https://goo.gl/maps/M6XnHj8VKfRdG5Ad7
You can see from the signage that it's a through road (residential roads
don't
have such signage).  You can also see from the houses in the background
that it
is a residential area.  In fact, those houses are about as densely packed as
anywhere in Cardigan. many of the residential roads are less densely packed.

To continue the example, during road works on North Road, traffic is
diverted along
Napier Street (residential), Napier Gardens (residential), Maes-yr-Haf
(residential),
Rhos-y-Dre (residential), Maes-Henffordd (residential) and Feidr Henffordd
(residential) to rejoin Aberystwyth Road.  It's possible for through
traffic to
take that longer route but it normally doesn't.  And it's even less likely
after
the speed limit along much of that diversion was dropped from 30 MPH to
20 MPH a couple of years ago.  Just to show that a residential road like
Napier Gardens has a lower housing density than Aberystwyth Road,
https://goo.gl/maps/5fGPgoiXQH7A8wkP7

I can see the argument that Aberystwyth road is also residential and
therefore
drivers ought to be more careful.  But that is indicated by mapping houses
along
it (or at least mapping it as a residential area).  Speed limits also
indicate that
drivers should be more careful.

As always, there are compromises to be made.  But in much of the UK (and
probably
much of elsewhere) mapping a road that is both a tertiary (or higher) route
and which
also has houses along it as residential is not the best way of dealing with
the
problem.

All in my opinion, of course.

-- 
Paul
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