by Steven Varner
The oldest roads usually follow very close to a railroad line. Often they are immediately adjacent to the railroad.
Old telegraph and telephone poles with glass insulators often mark the paths of old roads.
The oldest roads generally did not bypass towns, but were usually the main street of town.
Early community road building organizations did not have eminent domain since they did not usually represent the state government. Therefore, old roads usually follow sections lines in the township-range survey system. Expect the old road to zig-zag a lot.
The main auto trail routes along section lines would often have later curved cutoffs added to make the road turns easier as traffic increased.
Old roads often bear some variation of the name of the original road such as Lincoln Way, Old Hwy 80, Old Lee Highway, etc.
The oldest road between two towns is often more winding and has a name of one or both of the towns. For instance the oldest road between Springfield and Shelbyville would probably be "Old Springfield-Shelbyville Road" or "Springfield Road."
The oldest roads may still be dirt, or paved in Portland cement or brick. In some places one lane wide cement roads with no expansion joints represent the very oldest route.
Early highways rarely had deep road cuts. If you see that a highway has a deep cut, chances are good that the older road took a longer, more winding route bypassing that hill.
On old dirt highways in the West, the wash (dry creek) crossings were often paved in cement.
Ask elderly locals. They love to talk about the old days when they were kids, and they will often give you surprisingly accurate descriptions of the early road path. The old highway was the only way out of their town and carried a lot of traffic in older times. Volunteers in historical and genealogical societies are particularly helpful since they are generally long time residents.