[Tagging] Using restriction and restriction:vehicle for the same restriction relation should be discouraged

[easbar.mail at posteo.net]

Currently there are two ways to limit the vehicle types a relation 
tagged as `type=restriction` (turn restriction) affects. The first one 
enables the restriction for *all* vehicle types, but then excludes some, 
like:

restriction=no_left_turn
except=bicycle

The second one lists the vehicles for which the restriction should be 
enabled explicitly using something like

restriction:hgv=no_left_turn

Both ways seem to be useful and also represent what occurs on real 
street signs. For example there are some that restrict turns only for
hgv vehicles and others that restrict all vehicles with an exception 
like bicycle.

According to this schema one *could* use both approaches in a less 
obvious way, i.e. use the restriction tag when the turn is only 
restricted for a certain vehicle type like:

// here we like to restrict only hgv
restriction=no_left_turn
except=motorcar;moped;psv;bicycle;

or use the restriction:vehicle tag when the turn is restricted for 
almost every vehicle type like:

// here we like to restrict everything except bicycle
restriction:motorcar=no_left_turn
restriction:moped=no_left_turn
restriction:psv=no_left_turn
restriction:hgv=no_left_turn

Quite obviously this isn't ideal and as far as I can tell this is the 
exact reason we have the two approaches (one for excluding vehicles and 
another for including them). So using the right approach depending on 
the situation (or better depending on what is actually stated by the 
traffic signs) should be encouraged.

In some very rare cases even both approaches are used simultaneously. 
This leads to either redundant information or, even worse, contradicting 
tags.

I think the wiki 
(https://wiki.openstreetmap.org/wiki/Relation:restriction) should state 
that the restriction tag should not be used in combination with the 
restriction:vehicle tag. Is there any reason not to do this? For the 
except and restriction:vehicle tag maybe there should be a short note 
that these should be used when the restriction is valid for all but a 
few or only a few vehicles, respectively.