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

[Philip Barnes]

The ahead only restrictions you have added should work, will have to
wait until Tuesday to see if they have worked in OSRM.

Apart from the missing restrictions, its one of those strange routing
algorithm things. It is taking that route because it reaches the trunk
road in a shorter distance. 

OSM is based on the UK road classification system, so we have it easy. A
trunk road has green signs and usually but not always an A number (there
are B roads that are trunk), in other countries much discussion does go
into road classification and what is and isn't a trunk road.

Phil





On Sun, 2012-12-16 at 11:38 +0000, Sebastian Arcus wrote:
> I have a question about how to correctly trace highway links at 
> junctions/intersections. Sometimes a link physically crosses over one or 
> two other lanes coming from the other direction of traffic, before 
> reaching the lane it is suppose to merge into. Now, these junction 
> points do exist in real life, but from the point of view of navigation 
> software, they are useless as one is not allowed to turn turn into any 
> of those lanes of traffic it crosses until it reaches the right lane it 
> is supposed to merge into.
> 
> My question is, should these junction/common points between paths 
> actually exist in OSM? Wouldn't it be better to draw the highway link 
> like it wouldn't actually intersect with those oncoming traffic lanes - 
> and just joined it to the final destination lane? I use Navit GPS - and 
> it sometimes assume I can turn into those oncoming traffic lanes just 
> because the common waypoint indicates there is a joint. Maybe other GPS 
> navigation software does the same mistake?
> 
> In case my explanation is a bit fuzzy, I will give an example. The 
> following relatively simple junction is in Liverpool:
> 
> http://www.openstreetmap.org/?lat=53.394271&lon=-2.982713&zoom=18
> 
> Imagine you are traveling northwards on Sefton Street towards the 
> junction. The right-most link (looking northwards, in the direction of 
> travel) is obviously a no-no as it is a one-way going south. However, 
> Navit suggested for some strange reason that I take the middle link, and 
> then turn immediately left on the first lane of traffic that the link 
> hits into Chaloner St and continue northward. In real life, that is 
> impossible, because that particular highway link (the middle one) is 
> only for crossing over the first two lanes of traffic it encounters, and 
> then merging with the far most one and continuing east on Parliament Street.
> 
> My thinking was that if the middle link coming from Sefton Street didn't 
> have common waypoints/joints with the first two lanes, the navigation 
> software would have never had any reason to suggest such a move. Those 
> points are as good as non-existent in practice, as they can't be used 
> for turning left or right into those two lanes.
> 
> Could anybody with more experience weigh in on this with some pro's or 
> con's please.
> 
> Thanks,
> 
> Sebastian
> 
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