Thank you for reporting this to us, Mustang. Are you building the road on open ground or are you replacing old road with new road? Because in the latter cause you only get the difference between the culture. So if the previous road already gave you 10 culture, you would only get +10 with the Cobbled Road (because you keep the 10 culture from the old road, together it still makes 20).
I did build over existing road, Thank you. Didn't realize it would make a difference.
Will sell existing road and build new cobbled road instead. Appreciate your prompt
reply.