On the older Arkansas county maps published by AHTD (the old maps have far superior cartography than the current ones do) show the following types of roads in the legend: "concrete or bituminous pavement - high type"; "bituminous pavement - low type"; "gravel or stone road"; "graded and drained road"; "unimproved road", and "primitive road". What is the difference between high type and low type bituminous pavement? I have no idea why AHTD would group concrete with bituminous pavement, but they both use a solid black line. What is a graded and drained road?
The legend also shows the typical types of road: FAP, FAS, NFM (national forest maintained (county roads maintained by the forest service)), NFR (national forest road (built by and maintained by the forest service)), TAR (timber access road), and NFH (national forest highway). The NFH designations are marked along sections of state and US highways that go through the national forests. What is the significance of the NFH? These aren't forest service roads - they are roads built and maintained by AHTD. Was there some special kind of funding?
An example of an Arkansas county map from this era can be found at https://www.dropbox.com/s/33llata443rxcoh/mpolk_1983.pdf?dl=0
Presumably, high type would be asphalt concrete and low type would be chipseal. Concrete and AC would be grouped together because they're both durable surfaces capable of carrying high volumes of high speed traffic, where chipseal is generally used only for low volume, low speed roads. Graded and drained would usually mean that the road is crowned or sloped and has drainage ditches alongside it to allow stormwater to run off instead of pooling on the road, as would typically happen on an unimproved road.
Kentucky used to advertise its paving projects as either "high-type surface" or "bituminous asphalt surface."