[mkgmap-dev] Excessive routing time through roundabouts

Wed Sep 1 13:33:44 BST 2010

Hi

I'm not sure if this problem lies with mkgmap or elsewhere, but I've noticed
that my Garmin Nuvi seems to be avoiding roads with roundabouts generated
from OSM routable data, especially if there are multiple roundabouts. I did
some tests in Mapsource over a short 1.1 km route from S34 32.332 E150
51.412 to S34 32.541 E150 50.796 containing three roundabouts.

I generated a route using Worldwide routable Garmin maps (mkgmap.version
1568). Here are the route directions and times:

   Directions/Name                      Distance  Leg len  Leg time Total
time
1. 137 Reddall Pde                           0 m            0:00:00
2. Get on Reddall Parade and drive west      1 m      1 m   0:00:00
0:00:00
3. Enter roundabout Roundabout              69 m     68 m   0:00:04
0:00:04
4. Take the 2nd left onto Reddall Parade    94 m     25 m   0:00:16
0:00:20
5. Enter roundabout Roundabout             463 m    369 m   0:00:41
0:01:01
6. Take the 2nd left onto Reddall Parade   487 m     24 m   0:00:10
0:01:11
7. Enter roundabout Roundabout            1.0 km    519 m   0:00:50
0:02:01
8. Take the 2nd left onto Reddall Parade  1.0 km     36 m   0:00:20
0:02:21
9. 213 Reddall Pde                        1.1 km     67 m   0:00:22
0:02:43

As you can see, Mapsource has calculated that it will take 16 seconds to
drive through the first roundabout (distance 25m), 10 seconds for the second
roundabout (24m) and a whopping 20 seconds for the third roundabout (36m).
That last roundabout works out at a speed of 6.5 km/h -- I could just about
walk faster!

By contrast, using City Navigator ANZ NT 2011.1, the route between the same
points looks like this:

   Directions/Name                      Distance  Leg len  Leg time Total
time
1. 137 Reddall Pde                           0 m           0:00:00
2. Get on Reddall Pde and drive west         0 m     0 m   0:00:00   0:00:00
3. Enter roundabout Roundabout              70 m    70 m   0:00:06   0:00:06
4. Take the 2nd left onto Reddall Pde       99 m    29 m   0:00:05   0:00:11
5. Enter roundabout Roundabout             470 m   371 m   0:00:36   0:00:47
6. Take the 2nd left onto Reddall Pde      501 m    31 m   0:00:06   0:00:53
7. Enter roundabout Roundabout            1.0 km   510 m   0:00:49   0:01:42
8. Take the 2nd left onto Reddall Pde     1.0 km    37 m   0:00:10   0:01:52
9. 213 Reddall Pde                        1.1 km    61 m   0:00:07   0:01:59

As you can see the roundabout routing times are much more reasonable.

Is this excessive routing time through roundabouts a problem due to the way
these roundabouts are drawn in OSM, or is it mkgmap, or something else?

Ken.