OpenStreetMap
Registered with OpenStreetmap today and began edits. The first was a state road turned over to counties, and the remainder are county roads that are now named. I went over the US highway tag definitions, and settled on tertiary as the best match.
The problem is there's no exact match with the road system in the State of Georgia. Paved county roads tend to have the same width as state roads, and are heavily traveled, even in rural areas. Unpaved county roads can be heavily traveled as well, although they tend to be narrower. However, tract isn't a good match. Tracts tend to be what we call a "field road," or run through woods. Unassigned is probably a better definition than residential, which apparently is the default for Georgia county roads on OpenStreetMap.
My goal at this time is to work on the paved county roads first before moving to the unpaved. It's probably more accurate to describe them as tertiary.
Discussion
Comment from Sanderd17 on 20 January 2011 at 08:56
Residential roads is for roads in city centers or village centers, so where there are a lot of houses next to the road.
Unclassified is for narrow roads but with less houses around it, maybe a farm once in a while.
Tertiary is for roads where you can easily cross each other: where you don't have to slow down or leave the road to cross each other.
for unpaved roads where speed is limited because of the surface: you should use the track value. You can show drivable it is by using the "tracktype" key.
For roads that are too narrow for cars, highway=path is used. That is if you can't choose between highway=footway or highway=cycleway.
Comment from 42429 on 20 January 2011 at 10:32
Welcome to our project!
When TIGER data was imported in 2007, all other roads (tiger:cfcc = A41) have been automatically converted to "residential" which is definitively wrong.
The OSM classification of streets is roughly (!) following functional highway classification:
http://www.dot.state.ga.us/maps/Documents/rural/Telfair_FC.pdf
motorway = fast road with no at-grade intersections
trunk = fast road with some (!) at-grade intersections
primary = principal arterial roads (often equal to US roads)
secondary = arterial roads (often equal to state roads)
tertiary = collector roads (often equal to country roads)
unclassified = public roads (access to more than one house)
residential = urban roads
service = access roads (for one house, e.g. a single farm)
track = dirt roads (4WD only), usually not accessible for cars
+tracktype = grade1 (paved), grade2 (gravel), grade3 (dirt), grade4 (earth), grade5 (invisible)
Paved tracks may be used e.g. on a golf course or in a national park.
Comment from Boondoggle on 20 January 2011 at 18:26
Thanks. I wasn't aware of that DOT map. It's possible I'll have to bump some paved roads up to secondary, which opens another set of problems - some paved roads not shown with a higher classification on the DOT map have just as heavy traffic. However, some of the county roads (most, actually), are just barely wide enough for two cars to pass. Usually one driver has to stop and pull over as far as you dare to the ditch. Whether that's tertiary . . .