Points of intersection show the relationships between the tangents and curve groups in an alignment.
There are two types of points of intersection:
Explicit Points of Intersection
An explicit point of intersection is the point at which two fixed tangents meet on a horizontal alignment.
When an alignment is selected, an explicit PI is represented by a 
grip. An explicit point of intersection can be labeled, moved, deleted, or broken apart.
Implied Points of Intersection
An implied point of intersection is the computed point of intersection (PI) at an alignment curve or curve group. An implied PI indicates where tangents would meet if they were extended. An implied point of intersection can be labeled.
When an alignment is selected, the implied PI of two fixed tangents that are joined by a free curve or curve group is represented by a 
grip. When the grip is present, the PI can be solved, which extends the fixed tangents to an explicit PI.
The display of implied PIs is controlled on the Point of Intersection Tab (Alignment Properties Dialog Box).