Thinking of road system

Im putting together some modular pieces for some roads in an urban city environment but finding it a bit lacking. Ive been playing some GTA V the last few days to see how the roads might be built in there and not sure how they do it. Theres so much variation and they seem to blend roads into the environment really well and of course its not flat in a lot of places so that doesnt seem suited to modular pieces. I realize Rock Star games probably uses a different engine but I would love to hear how people think they put together such a large variety of roads together.

Ive seen people use the spline tool for roads but I dont just want to repeat the same piece of road over and over, id like to have a variety of roads coming togethet at different points blended well together so if anyone has any tips or ideas or knows of any good tutorials that might lead me in the right direction, I would appreciate it.