All paths, except those created using Guided Drive, are stored as a series of target points through which the vehicle is required to drive. The Dynamic Edit functionality incorporated in Autodesk Vehicle Tracking allows you to move the target points of a path, dynamically updating the path to reflect changes in position. Grip editing mode allows you to make all path adjustments interactively simply by picking and dragging grips.
If you edit the path in such a way that the vehicle cannot get from a given point to the next target, the remainder of the path will draw as a single line (red by default).