Curvature

Value	Description	Photo Example
Horizontal Curve	A horizontal curve is a section of roadway that changes the direction or alignment of the road. Horizontal curves are used to gradually transition between two roadways that intersect, allowing vehicles to turn smoothly instead of making a sharp cut.
Vertical Crest Curve	A vertical crest curve is a type of vertical curve that connects two inclined sections of a roadway to form a crest. Vertical crest curves are used to gradually transition between different grades of a roadway, allowing vehicles to negotiate elevation changes smoothly.
Vertical Sag Curve	A vertical sag curve is a gradual change in the slope of a roadway that connects descending grades to form a bowl shape. Vertical sag curves are used to gradually transition between different grades of a roadway, allowing vehicles to negotiate elevation changes smoothly.
Horizontal and Vertical Crest Curve	A horizontal and vertical crest curve is a combination of a horizontal curve and a vertical crest curve on a roadway. A horizontal curve changes the alignment or direction of a road, while a vertical curve changes the slope. A vertical sag curve is a type of vertical curve that occurs when a positive grade changes to a negative grade.
Horizontal and Vertical Sag Curve	A horizontal and vertical sag curve is a combination of a horizontal curve and a sag vertical curve on a roadway. A horizontal curve changes the alignment or direction of a road, while a vertical curve changes the slope of a road. A sag vertical curve is a type of vertical curve that occurs when a negative grade changes to a positive grade.
Multiple Horizontal Curve	A series of two or more back-to-back horizontal curves that are tangential.
Multiple Vertical Curve	A series of vertical curves that join multiple sloped grades along a highway.
Straight	Contains no horizontal or vertical curvature.

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[Supporting Notes to further explain any exceptions or special situations or to help provide further clarity]