Nikolai, great question. Having designed scenarios on occasion for various games, I have had the same question as you. I think there are two aspects worth mentioning.
The first, and more important, are how the road types affect game play. IMO, this issue is tied to geography (what area does the map depict) and the historical era depicted by the scenario. Consider West Germany in the 1980s. Every important road was hardened. Even county (Kreis) roads were hardened, if narrower than federal roads. The Autobahnen are in a class by themselves.
So perhaps some TOAW considerations here are things like supply flow, and the road's ability to bear heavy military traffic round-the-clock. Here are some notions:
Road Type Value as supply route Durability
Autobahn Very Good Very Good
Federal Road Good Good
Kreis Road Poor Poor
"Dirt" roads in TOAW have increased movement costs in conditions of mud. Big scenario design aspect there. In Alsace 1944-45, many of the "improved" roads were narrow and not very durable for military traffic. They often "broke" under the strain of U.S. military operations, and the U.S. Army always had bunches of engineer battalions in the rear keeping roads repaired and also improving them. So, although they were technically "improved" roads, should a designer depict them as "dirt" roads in TOAW? What about the Kreis roads in Germany of the 1980s?
IMO, it boils down to which supply and movement effects a designer wants for a scenario. Consider things like the new setting for movement costs on improved roads -- again, IMO, that is something for Autobahns and the like ... but if one wants to model that, does that force every other road to be a "dirt" road that is less capable just because of some heavy rain?
The second aspect is cosmetic. The dirt-surface, "squiggly" look of the regular roads in TOAW give a particular appearance that is not appropriate for minor paved roads -- yet again -- one has to recall the mud penalty. The look can be changed with a graphics mod, but I don't think the mud penalty can be turned off.
So, as to your question as the game roads reflect the "real world" ... the game gives us two basic road types, whereas in "real life" there are all kinds of roads in terms of military utility. My guess is that anything more sophisticated than that would require a lot of new code being written.
< Message edited by cathar1244 -- 2/26/2019 1:23:23 PM >