How to Use the Road Profile Grade and Design Elevation Calculator
Reading a road profile usually comes down to one question: what is the finished elevation at this station? The design elevation equals the elevation at the start of the tangent grade plus the grade multiplied by the distance run. Adding the existing ground elevation tells you immediately whether the station falls in cut or in fill.
Profile grade is expressed as a percentage, positive for an upgrade and negative for a downgrade. A 2.5% grade rises 2.5 ft for every 100 ft of horizontal run, so a station 400 ft ahead sits 10.00 ft higher than the start. The calculator also reports the equivalent run to rise ratio, which is the form used on typical section sheets and drainage details.
Cut and fill come from subtracting the design elevation from the existing ground elevation. A positive value means the ground is higher than the proposed surface and has to be excavated, while a negative value means material has to be brought in. Tabulating those values station by station is the first step toward an earthwork quantity takeoff.
Real profiles insert a vertical curve wherever two tangent grades meet, so elevations near the point of vertical intersection differ from the straight grade result. Vertical curve elevations require the curve length and the algebraic difference in grades, and the minimum curve length is set by stopping sight distance for the design speed.
Frequently Asked Questions
A negative value represents a downgrade, so the design elevation comes out lower than the starting elevation. The elevation change line labels the direction, which makes a mistyped sign easy to spot.
Existing ground minus design elevation gives the value shown. Positive means the ground sits above the proposed surface and has to be cut, negative means material has to be placed as fill.