It's finally done. A subway-style diagram of the major Roman roads, based on the Empire of ca. 125 AD. Creating this required far more research than I had expected—there is not a single consistent source that was particularly good for this. … The biggest creative element was choosing which roads and cities to include, and which to exclude. There is no way I could include every Roman road, these are only the main ones. I tried to include cities with larger populations, or cities that were provincial capitals around the 2nd century.
Obviously to travel from Petra to Gaza you would take a more or less direct road, rather than going to Damascus and "transferring" to the Via Maris. The way we travel on roads is very different from rail, which is a slight flaw in the concept of the map. But I think it's still aesthetically pleasing and informative.
There's maps for the empire at its height, and also more detailed local ones for Britain, Hispania, Gaul. All available as posters.