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I'm currently testing pgRouting using OpenStreempMap XML dataset loaded via Osm2PgRouting. My goal is to solve shortest path problems using time driven costs instead of path length.

I noticed that since V 2.1 osm2pgrouting include two nice columns namely cost_s and reverse_cost_s. They aim to express cost in seconds. Theses columns are computed using maxspeed_forward maxspeed_backward properties.

When the OSM dataset include maxspeed attribute you can expect reasonable results. However when theses tags are not filled a default value is applied (controlled by the config.xml file).

This lead to very high maxspeed values in residential area when the road type is set to primary/secondary/tertiary. But 90Km/H inside a town really doesn't sound realistic.

Has anybody already have a fix for that kind of behavior?

I was thinking about setting a lower maxspeed for road that intersect landuse=residential in OSM. Am I reinventing the wheel or is it something to look at?

  • What's wrong with just setting the maxspeed yourself for these roads? That should be very quick. If you have an idea of what a reasonable value should be, and if there is no OSM data on maxspeed, you will probably get better results than using the default. – amball Sep 20 '16 at 18:26
  • This is what I'm currently doing. And I'll post my method here if I there is no other answer. Thing is I must not be the only one that stumble into that problem so maybe there is already a known solution out there. Plus in the spirit of OSM the ideal would be to improve the master database so that everybody profit from theses tweaking. This was more like a bottle thrown into the sea. But perhaps my message is unclear feel free to suggest improvement ;) – MarHoff Sep 21 '16 at 8:07
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Here is my quick-fix assuming you have downloaded from OSM all polygon with the tag landuse="residential" in the working area of your network. Thoses polygons are stored under the table "landuse_residential" in my DB.

  1. Intersect the two layers to finds ways in a residential area

    WITH intersect_residential as (
         SELECT distinct(ways.gid) as gid_select FROM ways, landuse_residential
         WHERE ST_Intersects(ways.the_geom,landuse_residential.geom) AND st_isvalid(landuse_residential.geom))
    
    UPDATE ways SET rule='residential' FROM intersect_residential WHERE gid=gid_select;
    

    Notice I am storing the result in the ways.rule column because i literally have no other use of it. You may want to create a new column to store result depending on you use case.

  2. Update maxspeed columns according to residential area

    UPDATE ways SET
       maxspeed_forward=LEAST(maxspeed_forward,50),
       maxspeed_backward=LEAST(maxspeed_backward,50)
    WHERE rule='residential' AND class_id NOT IN (101,102,103,104,105);
    

    I'm setting maxspeed as an upper limit according to my country laws, if a lower limit have been set I got to keep it using LEAST(). Please notice that I exclude road class like motorway & trunk because even if they appear in urban area you can expect that they are ruled by specific speed limit, so it would be very unwise to affect a standard town speed limit.

  3. Update cost_s and reversecost_s according to new max_speeed

    UPDATE ways SET
          cost_s = CASE 
                   WHEN one_way = -1 THEN -st_length(geography(ST_Transform(the_geom, 4326))) / (maxspeed_forward * 5 / 18)
                   ELSE st_length(geography(ST_Transform(the_geom, 4326))) / (maxspeed_backward * 5 / 18)
          END, 
          reverse_cost_s = CASE 
               WHEN one_way = 1 THEN -st_length(geography(ST_Transform(the_geom, 4326))) / (maxspeed_backward * 5 / 18)
               ELSE st_length(geography(ST_Transform(the_geom, 4326))) / (maxspeed_backward * 5 / 18)
          END 
    WHERE rule='residential' AND class_id NOT IN (101,102,103,104,105);
    

    Using formulas accordingly with this part of the source code and this related issue

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