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.