[OSM-talk] Routing Applications

[Maarten Deen]

On 2015-06-17 15:08, Michał Brzozowski wrote:
> On Wed, Jun 17, 2015 at 2:55 PM, Eugene Alvin Villar <seav80 at gmail.com> 
> wrote:
>> Imagine a single-carriageway road crossing a dual-carriageway road.
>> All turns are allowed except u-turns from one side of the
>> dual-carriageway to the other. This common situation can only be
>> modeled using a turn restriction with a via way.
>> 
>> Now if the via way had to be split for any reason, then you have
>> multiple via ways.
> 
> Isn't the restriction type (no_u_turn, no_left_turn, no_right_turn)
> basically just for display purposes? Because given from, to and via it
> only matters whether it's no_* or only_*.
> 
> The solution I think is going to give correct routing would be to make
> a no_u_turn where one of the carriageways is from, the node at
> intersection is via and that small connecting segment is to.

No, because then you also restrict left (or right, in LHD countries) 
turns.

Imagine this situation (ASCII art):

+------6------8------1------+
               |
               2
               |
+------5------9------3------+
               |
               4
               |
               +

Driving from way 1 to way 3 is not allowed (U-turn). Making a turn 
restricting from  way 1 to way 2 via node 8 prohibits driving from way 1 
to way 4 also. You have to make a restriction from way 1 to way 3 via 
way 2.
I think you are right in saying that the type of restriction is only for 
display and has no real purpose for the router.

Maarten