Used to construct a parabolic fillet (curve element) between two lines.
You can access this tool from the following:
 Ribbon:
split button
 Toolbox:
Fillets
Setting  Description 

Distance 
The distance between the points of tangency. 
Type 
Sets how the parabola is aligned:
 Horizontal — aligned with the horizontal view axis. Used in highway design to join intersecting grade lines. All IGDS parabolas are horizontal.
 Symmetric — aligned with the selected lines.

Truncate 
Controls which line(s) are truncated.
 None — neither line is truncated.
 Both — both lines are truncated at their point of tangency with the fillet. If a fillet is constructed between two closed elements or an open and a closed element, the closed element(s) are not modified.

Note: In 3D, for two both elements to be filleted, they must be on the same plane.
To place a Bspline curve in the form of a parabola, use the Conic Curve tool.
Keyin:
PLACE
PARABOLA
[
HORIZONTAL

MODIFY

NOMODIFY
]
[
MODIFY

NOMODIFY
]