On Tue, Feb 26, 2019 at 9:40 AM Paul Allen <pla16...@gmail.com> wrote: > > On Tue, 26 Feb 2019 at 12:17, Fernando Trebien <fernando.treb...@gmail.com> > wrote: >> >> >> I don't think a uniform, worldwide highway class standardisation based >> on road attributes is possible and satisfactory. But I think a >> functional one would be, at least as a guiding principle. > > > What we currently have doesn't reflect reality too well, even in the UK. It > makes the > assumption that the width/capacity/speed of a road correlates well with its > classification. > Of course, we have lanes and speed limits to refine matters, but there is > still the implicit > assumption by many mappers that a primary route is "better" than a secondary > route.
This leads me to this question: if we can map road attributes using specific tags (width=*, speed=*, lanes=*, surface=*, even divided=* which is currently represented by geometry), then why highway=* has to correlate strictly with them? I think highway=* is intended to represent something else, not what mappers commonly think, though the two would be correlated. > It's sort of true, in the UK, most of the time. But it is possible for a > primary route in the UK > to have fewer lanes or lower speeds for part of its length than a secondary > route between the > same two locations. Unlikely, but possible. Road classifications in the UK > are essentially > hints to the routeing algorithm in drivers' heads. A primary route from A to > B is generally > preferable to a secondary route because of a combination of factors including > speed, width, > straightness, length, junctions (lights or roundabouts), surface, and > signage. On any single > one of those metrics the secondary may be better than the primary, but > overall the primary > is preferable. A secondary route in one locality may be better in all > respects than the primary > in a different locality but that route is a primary because it is the best > route (for some values > of "best") betweentwo important locations. There's a very interesting similar situation near the place where I live in Brazil. There are two main routes between a metropolis of 4 million people (Porto Alegre) and the second largest city in the state (Caxias do Sul), which are 2 hours apart from each other: the shorter federal highway, and a longer string of three state highways. Both are paved, but the state highways are divided and higher speed, while the federal highway contorts through hilly terrain. As a result, the state highways are the main route between the two, so, there's consensus that in this particular case the federal highway is not as important and the state highways should be classified as more important than that one. A while ago I crunched some numbers and revealed that paved federal highways highly correlate with the functional trunk class as published by some local authorities, though the correlation is not exact. So if we were classifying based solely on attributes, we would have achieved a result that is not in line with consensus in this rather significant case, though it would mostly agree in general. -- Fernando Trebien _______________________________________________ Tagging mailing list Tagging@openstreetmap.org https://lists.openstreetmap.org/listinfo/tagging
