There actually is one entry for roads, but it wasn't called roads, rather something like transportation or similar. The text then contains a hyperlink which is labelled "roads", but it just links to itself.
Stumbled across it while trying to figure out if all those roads I was building before researching paved roads did cost money as well.
(In the end I just loaded an older save game to check, and yes they do.)
// Edit
Just checked, it's Game Concepts/Movement. There's a "Roads and "Railroads" entry with hyperlinks to each of both, and each of both just link to same page (itself).