What I try to say is that you should not map a important road for large distances as "secondary + works_as_primary" just because it is a smaller, has a different surface, a different ref or whatever. Then (large distance, important road) it is a primary road IMHO, regardless of any other tags.
If one downgrades such a road to secondary, the router can no longer prefer it over other (real secondary) roads. (as you wrote) Perhaps Ralph Aytoun expressed it better. But I tried to say the same as he. Of course we shouldn't tag secondary or primary roads as trunk road or motorways, but secondary & primary roads should only be tagged based on their function, not on their appearance. regards m On Wed, Jul 29, 2015 at 1:11 PM, moltonel 3x Combo <molto...@gmail.com> wrote: > On 29/07/2015, Marc Gemis <marc.ge...@gmail.com> wrote: > > On Tue, Jul 28, 2015 at 5:29 PM, moltonel 3x Combo <molto...@gmail.com> > > wrote: > > > >> A router won't care about classification differences between far away > >> places like Germany to Ethiopia. They just care about taking the best > >> road in the area, and as long as OSM is locally consistent, this > >> works. Even if a trunk turns into a primary for no physical reason and > >> > > > > Seems like I didn't make my point correctly. > > I was trying to ask for global consistency so the router can use the same > > default weights for street types, everywhere in the world. Something > like > > 'prefer primary roads over secondary' roads to travel large distances. > > Routers can already use 'prefer primary to secondary' worldwide. > Nowhere in the OSM world is secondary defined as better than primary. > In any given area. a car router can confidently prefer 'primary'. > > What's true is that 'primary is X times better than secondary' will > have different X values from one place to the next. But the > differences between section of a given road can already be more > important than the average difference between primary and secondary > (for example an Irish secondary´s maxspeed can go from 60 to 100, but > a primary isn´t generally 1.6x better than a secondary). > > Consider also the case of motorways : in all countries I've driven in > they are very clearly defined and have legal specificities. OSM > couldn't afford to mistake a motoway with something else. Yet the > difference between a motorway and the next best thing is bigger in > Germany than in Ireland. > > TD;DR: It's naive to think that routers can make a good decision using > the highway tag alone. Harmonising highway tag worldwide would be of > little use, and it would break local expectations. A locally coherent > highway tag is preferable, and if you want more precise routing add > the other tags. > > _______________________________________________ > Tagging mailing list > Tagging@openstreetmap.org > https://lists.openstreetmap.org/listinfo/tagging >
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