You can change the tangency and parameter constraints of alignment lines, curves, and transitions.
When you create an alignment, you define the geometry of each line, curve, and transition by specifying a set of parameters, or constraints. After an element is created, you can only edit the parameters that affect the specified constraints. The alignment layout honors the constraints, even if the geometry of adjacent elements is changed.
As you edit the alignment, you can change the constraints for each element as needed.
There are two types of alignment constraints that you can change:
Tangency Constraints
A tangency constraint is a parameter that can constrain an entity's geometry to the geometry of an adjacent entity.
There are four tangency constraints:
Not constrained (Fixed) 
Constrained by Preceding (Floating) 
Constrained by Following (Floating) 
Constrained on Both Sides (Free)
The manner in which an element can be edited may be restricted by its tangency constraint. For example, an element that is constrained on both sides will always maintain tangency to the elements that are immediately before and after it, even if one of the adjacent elements is moved.
You can specify that if an entity's tangency constraint is changed, the tangency constraints of adjacent entities will be changed so that tangency is maintained.
Parameter Constraints
Parameter constraints are the parameters by which an element was constrained to when it was created. Following are examples of parameter constraints:
- pass-through points
- radius
- length
- angle
Parameter constraints may be locked for either each element, or for all elements in an alignment.
- Locked: The Parameter Constraint cannot be changed. Only the parameters permitted by the Parameter Constraint can be edited.
- Unlocked: The Parameter Constraint can be changed, which enables a wider variety of parameters to be edited.