I'm currently working on a small program that evaluates OpenStreetMap data to calculate how twisty or curved roads are in order to generate maps of roads that may be of interest to motorcycle riders or other driving enthusiasts: https://github.com/adamfranco/curvature/wiki
The major limitation I've found is a dearth of road surface data that indicates whether roads are asphalt, concrete, gravel, or at a minimum paved/unpaved. Are there any non-proprietary data sets that contain this information for either the whole US or particular states? The TIGER dataset doesn't seem to contain road-surface information as far as I can tell.
Best Answer
TIGER 2010 has the
MTFCCWhich is Classes with a code - S1100 for Primary Road (Highway)
You can investigate the codes S1500 - Vehicular Trail (4WD)
S1820 Bike Path or Trail
S1830 Bridle Path
*this might not be a perfect classification but a starting point
Full comprehensive list in Open Street Map
http://wiki.openstreetmap.org/wiki/TIGER_2010