[OSM-talk] [Tagging] - RFC - Motorway_linkimpliesoneway=??

[Philip Homburg]

In your letter dated Mon, 6 Oct 2008 19:04:28 +0100 you wrote:
>2008/10/6 Matthias Julius <lists at julius-net.net>:
>> "Stephen Hope" <slhope at gmail.com> writes:
>>
>>> Bad assumption.  This may be the case in parts of Europe and the USA,
>>> but certainly not in most parts of the world.
>>
>> Maybe not in most parts of the worlds, but most trunk roads. ;-)
>
>I know that the German mappers have decided that "trunk" is a handy
>extra road category that can be used for Schnellstra=DFen. I also know
>that other countries find it a useful classification for similar
>purposes. But the country whose road system gave us the "trunk" tag
>has thousands of km of standard single-carriageway road that bears the
>tag. I would assume that oneway sections are in the minority in the
>UK. In Ireland they certainly are.

I wonder if it would be worth while setting up a wiki to collect the
legal definitions of road types in the various countries.

For example, the Dutch traffic regulations do not say anything about whether
is motorway is dual-carriage or not. However they are explicitly one-way.
So the Dutch equivalent of a trunk road is usually a single-carriage way but
it is also oneway. 

However, in this case the oneway-ness is more or less irrelevant for OSM.
It only means that you can't turn on the road, and that you can't drive in
reverse.

In practice, all Dutch motorways are dual-carriage. So it makes sense to 
assume oneway-ness by default. 

For trunk roads, it might be just a safe default to assume that the way is
oneway, unless tagged explicitly as single-carriage (oneway=no).