Many times i wonder what is correct road type to set while drawing roads on OSM.
I have seen code of few (offline ) navigation software like OSMAND, which use following criteria while calculating ETA if no Max speed is specified.
Motorway 110KM/H
Trunk Road 80KM/H
Primary 65KM/H
Secondary 50KM/H
Tertiary 35KM/H
Minor and below 20KM/H
Currently I am updating all road types considering average speed on that road (Traffic and other aspects). This helps me to get approximately correct ETA on navigation systems.
Please let me know if we should follow other techniques or Logic to decide road type.
Hi Rahul, highway classifications are meant to signify road hierarchy and importance. Please see the osm wiki on the standards we currently follow in India:
http://wiki.openstreetmap.org/wiki/India:Tags/Highway
Following this guideline will ensure data consistency through the database. You can indicate speedlimits using the ‘maxspeed’ tag.
By setting road classification based on speed limits, you are exposing the data to inconsistencies. Speed limits are subject to change often with rod upgradation, this does not affect the importance of a road. Also, the speed limits you have mentioned is due to a certain program being configured in a specific way.
Do revert your road classification edits to the original ones. This issues has been discussed on the mailing list in the past and the general agreement is to follow the guidelines proposed in the link above. Let me know if you think the tagging guidelines need to be changed.
Ok I Understood.
I will start reverting back those changes but it will take some time… as it was not done in 1 day. 
I will follow all standards mentioned in http://wiki.openstreetmap.org/wiki/India:Tags/Highway
Thanks.
You can also add some tags specific for the mkgmap renderer: mkgmap:road-class and mkgmap:road-speed.
“maxspeed” is the (legal) maximum speed on the road, and often the normal cruising speed is far less.
And of course, when you create the map yourself, you can use other tags than highway for the main categorization of the roads shown. For some countries, such a different handling is not only useful, but actually necessary.
The standard rendering is optimized for countries with a highly developed road network, and also here some problems do occur.
Just look at this photo (taken in Germany): http://www.panoramio.com/photo/74262774
On a typical map, you won’t be able to see that it is a really bad road - it will look like a “normal” unclassified or service. By the way, maxspeed for that road is 100 kilometers per hour - do not try that!