[Talk-us] Trunk VS primary,

[Richard Fairhurst]

Eric H. Christensen wrote:
> The routing engine should be able to take into account 
> the road surface

It can and often does. Your problem there is that only 2% of highway= ways
in the US are explicitly tagged with surface; probably only 30% are
implicitly tagged; and sometimes the implicit stuff gets broken, like when
people start retagging gravel roads as secondary without adding a surface
tag. (Numbers are estimates but I think not far off.)

> Any idea why trunk was established in the first place? 

It's a word from the UK road classification system, because OSM was invented
in the UK. But the letters in the word aren't really important.

OSM has five broad-brush motor-road tags (trunk, primary, secondary,
tertiary, unclassified), plus special-case ones at either end of the
hierarchy (motorway for limited-access high-speed roads, residential for
roads with the main purpose of providing access to houses on that road). If
you don't think you need five, you don't need to use all five. If you need
more than five, you are free to use additional tags to supply extra nuance,
as the Germans do with motorroad=yes. I would say that 15 years is probably
more than enough time to decide what roads you're putting in what category,
but hey, this is OSM.

Richard



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