By default CityEngine uses OSM data and applies a set of heuristics to create street geometry. What you can do: After downloading OSM data you get a window that lets you turn off "Run generate bridges", "Run Simplify Graph.." and "Run Graph Clean Up..." this can result in a more satisfactory import.
Hope this helps, Chris
I am going to go against the grain and say I no longer do this in CityEngine. Christian Iten has great suggestions for doing this work in CityEngine, but if you feel like GIS is your real pocket knife I would do the work there.
The tools I typically use include:
4. Sometimes: https://github.com/d-wasserman/feature-line-split (Feature Line Whiskers to get width attributes from other datasets).
Editing in GIS is just easier, and the tools to deal with attribute changes from dual carriage ways are just easier to manage there. If you go with a large enough study area, a cross-sectional database is just easier to maintain in GIS. Once imported, then I make sure everything is positioned with the tools mentioned here.