This means that Feature Lines will interact with other Feature Lines that are included in the same Site.

First you need to know that Feature Lines are included in Sites in Civil 3D. With Feature Lines in Civil 3D you can now safely create crossing Feature Lines and you may even want to do it intentionally once you learn how to control them. However, this was a scenario that was a common problem for many users. If you were careful and made sure to snap those 3D polylines together at the point they crossed so that the lines were crossing at exactly the same elevation then you were OK. One of the scenarios that users always tried to avoid when grading with 3D polylines was creating 3D polylines that crossed which in turn created crossing breaklines. Feature Lines in Civil 3D were originally based on the concepts and tools that many of us used in Land Desktop by grading with 3D polylines and then adding functionality that we could only wish for in LDT.

Using Feature Lines for grading in Civil 3D has been an area of the program that has continued to evolve with each release.

Civil3d grading