[Tagging] How to tag correct number of lanes for freeway on/off ramps?

[Matthew Woehlke]

On 03/07/2020 17.53, Paul Johnson wrote:
> On Fri, Jul 3, 2020 at 3:19 PM Matthew Woehlke wrote:
>> Consider https://www.openstreetmap.org/#map=17/42.85888/-73.77169. As I
>> write this, I-87 is annotated as having 3 lanes south of the on/off
>> ramps (south of 146). However, the off ramp starts all the way back at
>> the Sitterly Road overpass, and the on ramp doesn't fully merge until
>> just before the emergency vehicle turn-around only slightly north of
>> said overpass. Accordingly, there are actually four lanes for these
>> stretches.
>>
>> What is the correct way to model this?
> 
> It's hard for me to explain so try the example in
> https://www.openstreetmap.org/changeset/87518597#map=14/42.8442/-73.7720 on
> for size?

Thanks! In particular, TIL about the `placement` tag. Actually, the 
proposal page for that is rather helpful.

A couple notes, though: you missed a transition, and IIUC, the `turns` 
should instead be `|||slight_right`, since there is no explicit 
'straight only' marking. (Strictly speaking, there is no *explicit* 
marking for 'slight right' either, but it's implied by the fact that 
you're in a turn lane. I wonder if we should have a way to tag that 
separately? Anyway, I would hope that having the lane so tagged — I also 
tagged the on ramps |||merge_left — will encourage tools to not 
gratuitously route into those lanes only to need to leave them 
immediately, i.e. a better and more correct version of merge prohibition.)

Anyway, I hopefully cleaned up most of the stuff for the on/off ramps 
here. (Hmm, I skipped the north-most on ramp though, maybe I'll do that 
one later.)

It seems I need to take a look at JOSM, I've been wanting something that 
actually renders lanes... BTW, my "ultimate" goal, potentially, is to 
have fully and correctly modeled lane placement and connectivity. I'm 
working on traffic simulation with SUMO and basically need to be able to 
do perfect imports from OSM without having to clean up the network 
afterward. Plus, it can't hurt routing engines for this stuff to be correct.

-- 
Matthew