Dunwich was a tiny village to begin with and shrinking since early 19th century. You end up there by "taking the wrong fork at the junction of the Aylesbury pike". I'd say the Arkham-Aylesbury road is the only one that might be paved due to industrial traffic. Within Dunwich, a few main roads should be improved (that is, gravel) and the rest unimproved (dirt). Then it obviously shrinks down to dirt tracks and barely visible paths.
My favourite source book tells that especially the small roads can be in awful condition, thanks to snow, water and being in hilly terrain where woods are quick to take back whatever has been cleared. Autos struggle to climb the hills, get stuck in mud, and break their suspension to potholes and rocks. That might sound familiar to anyone living in rural Scandinavia or similar latitudes. A majority of farms would probably trust horses instead, especially during the worse seasons.
I don't think anyone would have bothered to make a paved road there, even in the village itself. Gravel roads are actually more reliable and easier to maintain if you have low resources at your disposal. Besides, Dunwich has been going mostly downhill in the days when the road network was being improved for cars so any paving projects were probably skipped there. I can check the book when I get back, but from memory the division was basically "improved" and "bad".