For real life planning, many concept in Cities Skylines are also in professional software. e.g. in Autodesk Infraworks you can import roads, drag out a spline f

For real life planning, many concept in Cities Skylines are also in professional software. e.g. in Autodesk Infraworks you can import roads, drag out a spline for a new metro line, then run a simulation to see the affect on traffic and other transport infrastructure.