[OSM-newbies] Question about how to connection correctly highway links

[Philip Barnes]

Hi Sebastian

> Thanks for the extra info. I will download a fresh copy of maps for 
> Navit with the restrictions in place to make sure that junction works as 
> expected. I kind of figured out Navit's navigation must have thought 
> that route would have been shorter or better somehow - but in real life 
> it wouldn't have been a viable one.
Routers do seem to overuse road classification, it works with motorways
but in built up areas classification is largely irrelevant. In the
example you gave Navit is assuming that the trunk road is faster, even
if its just by a second or two. In this case it wont be faster. Even if
it was legal, there is a 90 degree turn.

> 
> I must admit I haven't figured out yet the business with trunk roads - I 
> always sort of assumed based on OSM's wiki that "A" roads in UK are 
> primary highways - clearly I must go back and read the OSM highway 
> classification again. 
You do need to read the OSM wiki page, WikiProject United Kingdom A and
B Roads at
http://wiki.openstreetmap.org/wiki/WikiProject_United_Kingdom_A_and_B_Roads

Quote from the page:
In the UK, the OSM rule goes like this:

    green signed A roads: highway=trunk
    black-and-white signed A roads: highway=primary
    B roads: highway=secondary 

(It might sound confusing if you're used to hearing A roads described
differently. Sorry, it's just how we do things round here.) 
/end quote


> It doesn't quite help the fact that tertiary 
> highways correspond to "C" roads, and secondary highways correspond to 
> "B" roads - thus living primary highways without a direct correspondent 
> in UK.
Tertiary roads are a bit of a black art, there are very few C roads
numbered on the ground and unless you have access to council info you
will not easily get hold of the numbers.

I tend to tag the main unclassified roads through an area as tertiary,
the ones that are used by through traffic, but I may be wrong. 

Regards Phil