You can find a map of known Roman Roads here. If you chose google maps as a basemap, you can see that many existing highways follow the routes of Roman roads almost exactly, showing nearly perpetual use up to the present.

That said, there is definitely a breakdown both in the quality of the Roman road and its usability. Mapping out coin finds from late antiquity to the Carolingian period, we can see a slow shift from known roads to rivers as waterways become the more reliable and rapid modes of transportation. This is not only due to the actual physical condition of the road, but the existence (or not) of facilities along that road which faded after the fifth century.