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. 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. Is this a good way to model thing? Probably. Because anyone in the UK looking to get from A to B will consider primary routes first, trusting that the authorities have evaluated matters and that the primary routes are (normally) the best routes to choose. It's not perfect, which is why satnavs usually offer the choice of looking for the fastest or shortest route. But if all you have is a paper map, then knowing which are primary and secondary routes is useful. -- Paul
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