[OSM-talk] Divided roads proposal

[Steve Bennett]

On Fri, Dec 4, 2009 at 4:54 AM, Anthony <osm at inbox.org> wrote:

> On Thu, Dec 3, 2009 at 12:38 PM, Steve Bennett <stevagewp at gmail.com>
> wrote:
> > Well, put it this way: if this was implemented, I would duplicate far
> > fewer roads in future.
>
> If it worked (and I really haven't delved into the details enough to
> check), I might be convinced to add division information where I
> otherwise wouldn't bother (because the current method of creating a
> dual carriageway is a pain).
>

Exactly.


>
> > If a router ignores the tags, it will occasionally try and send you
> > through a barrier.
>
> For a U-turn?  Whether or not a U-turn is legal should probably be
> treated as "unknown" by routers in most cases.  We're currently not
> really mapping that at all.
>

I guess that's country specific. Here (Australia), u-turns are legal by
default. But I'm not sure why routing software would need to do u-turns in
general.


>
> OTOH, if you're talking about a left turn, I thought the point was
> that this would be handled by turn restrictions just like would be
> done currently.
>

I'll assume you're in a right-hand-side drive country? Let's take this
situation:

       B
       |
A==============C

You're going from A to B. I'm saying that the router doesn't attempt to make
the turn because the way A-C is marked as divided=median, and there's
nothing at the intersection to overrule that. If left turns are possible
there, then the junction should be marked as a gap, or there should be a
section of non-divided at that point.

Turn restrictions are a pain to edit, so it's great that the router gets a
free hint here.


Yeah, I see this as maybe a potential solution in between using a
> single unmarked way and using a dual carriageway.  Although, looking
> at the proposal, it doesn't look finished - something you seem to
> admit yourself.
>

Yep, I didn't write that proposal, I just liked the ideas in it. I guess
tomorow I'll write up the summary of this discussion.

Steve
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