_link roads speed limit needs increasing
Travelling down highway 32, then 329 in Thailand recently I was told to do a U-turn, then use a dirt track, rather than the ramp that linked to h'way 329. Try routing yourself in Mapsource or Basecamp at N14 27.106 E100 32.322. It should look like something in this pic: https://dl.dropbox.com/u/30711166/OSM.T.jct.32-329-route.prob.jpg The route chosen by both GPSr & Mapsource is actually longer than simply following the ramp, but it avoids the ramps. The ramps were drawn as secondary_link which in the Garmin map becomes low-speed ramp with speedlimit 20 and RC=2. The U-turn is a trunk_link => principal h'way, SL=90, RC=4. The dirt track has SL=20, RC=0. It looks like the Route Class is less important here than the SL: by following the main route you only travel for a short distance over a slow road (the track), whereas the ramps are quite long. Mathematically this would make for a quicker trip. To avoid people being routed off main highways I propose that ramps mapped from secondary_link get the same SL as secondary and that the speed limits on the other links are reviewed. Regards, Peter.
The ramps connect a secondary to a trunk. Hence, I'd tag them as trunk_link, not secondary_link. That could result in correct routing. But in the Bing images, the "dirt track" looks more like a residential, which could contribute a contrary effect. Since the ramps are very long in that special case, setting a speed limit explicitly might also help. Maybe the Garmin device did not reognize that U-turn correctly, or the "penalty" for a U-turn is to small. Which tags are required that a U-turn is recognized as a U-turn? Kind regards, Bernhard Am 03.08.2012 02:12, schrieb Peter Hendricks:
Travelling down highway 32, then 329 in Thailand recently I was told to do a U-turn, then use a dirt track, rather than the ramp that linked to h'way 329. Try routing yourself in Mapsource or Basecamp at N14 27.106 E100 32.322. It should look like something in this pic: https://dl.dropbox.com/u/30711166/OSM.T.jct.32-329-route.prob.jpg
The route chosen by both GPSr& Mapsource is actually longer than simply following the ramp, but it avoids the ramps.
The ramps were drawn as secondary_link which in the Garmin map becomes low-speed ramp with speedlimit 20 and RC=2.
The U-turn is a trunk_link => principal h'way, SL=90, RC=4.
The dirt track has SL=20, RC=0.
It looks like the Route Class is less important here than the SL: by following the main route you only travel for a short distance over a slow road (the track), whereas the ramps are quite long. Mathematically this would make for a quicker trip.
To avoid people being routed off main highways I propose that ramps mapped from secondary_link get the same SL as secondary and that the speed limits on the other links are reviewed.
Regards, Peter.
On 6/08/2012 0:25, Bernhard Hiller wrote:
The ramps connect a secondary to a trunk. Hence, I'd tag them as trunk_link, not secondary_link. That could result in correct routing.
While I agree with that it wouldn't solve the problem if the ramps connected two secondary roads.
Since the ramps are very long in that special case, setting a speed limit explicitly might also help.
It might work, but doesn't address the fundamental problem that the ramps' default speed limit is lower than that of a dirt track.
Maybe the Garmin device did not reognize that U-turn correctly, or the
Mapsource routes the same.
"penalty" for a U-turn is to small. Which tags are required that a U-turn is recognized as a U-turn?
I'm afraid I haven't been able to find an answer to that question. I suspect that it doesn't work on dual carriageways with non-NT maps. Ramps created from trunk_link have a higher speed limit and I think that the other _link roads should also have them, for the same reasons. Kind regards, Peter.
participants (2)
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Bernhard Hiller -
Peter Hendricks