Vertical Curve Design
 
 
 

Designing vertical curves in layout profiles requires that you understand the concepts described in this topic.

Curve Types

K-Value

This value represents the horizontal distance along which a 1% change in grade occurs on the vertical curve. It expresses the abruptness of the grade change in a single value. Speed tables or other design tools often provide a target minimum K value.

The criteria-based design feature automatically validates profile curve design against local design standards. A.A.S.H.T.O. tables defining minimum K values at given speeds are provided in the customizable design criteria file. Curves that violate your design standards can be corrected by using the Profile Layout Parameters dialog box to either adjust K value directly, or change curve length and tangent grade to meet the criteria.

K-value formula

Stopping Sight Distance

This design method for crest curves provides a minimum curve length. The curve must be long enough so that the driver of a standard vehicle can always see an object before it gets within the maximum stopping distance for the designed speed of travel.

Diagram of stopping sight distance

Passing Sight Distance

This design method for crest curves provides a minimum curve length. The curve must be long enough so that the driver of a standard vehicle can always see an oncoming vehicle within a safe distance for the designed speed of travel.

Diagram of passing sight distance

Headlight Sight Distance

This design method for sag curves provides a minimum curve length. The curve must be long enough so that in dark driving conditions, the headlights of a standard vehicle illuminate the road a safe distance beyond the stopping distance for the designed speed of travel.

Diagram of headlight sight distance

Rider Comfort

This design method for sag curves provides a minimum curve length. The curve must be long enough so that people in a standard vehicle do not experience excessive inertial force as they travel through the curve at the designed speed.

Diagram of rider comfort design