How To Calculate Superelevation For Horizontal Curves In Excel PORTABLE
How to Calculate Superelevation for Horizontal Curves in Excel
Superelevation is the amount of rise seen on an angled cross-section of a road given a certain run, otherwise known as slope. It is used to design horizontal curves that allow vehicles to negotiate a turn at a gradual rate rather than a sharp cut. Superelevation also helps with drainage and reduces the side friction between the tires and the pavement.
How to Calculate Superelevation for Horizontal Curves in Excel
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In this article, we will show you how to calculate superelevation for horizontal curves using a spreadsheet tool in Excel. You will need to know the intended design speed, the coefficient of friction, and the radius of the curve. You will also need to download the Horizontal Curve (Superelevation Calculation Sheet).xls file from our website.
Step 1: Enter the input data
Open the spreadsheet file and go to the "Input" sheet. Enter the following data in the corresponding cells:
Design speed (V) in km/h
Coefficient of friction (f) (typically 0.15 for dry pavement)
Radius of curve (R) in m
Lane width (W) in m
Number of lanes (N)
For example, let's assume we want to design a horizontal curve with a design speed of 80 km/h, a coefficient of friction of 0.15, a radius of 300 m, a lane width of 3.5 m, and two lanes. We enter these values in the spreadsheet as shown below:
Step 2: Calculate the superelevation
Go to the "Output" sheet. The spreadsheet will automatically calculate the superelevation (e) using the following formula:
Where:
e = superelevation
V = design speed in km/h
f = coefficient of friction
R = radius of curve in m
g = acceleration due to gravity (9.81 m/s)
The spreadsheet will also convert the superelevation from decimal to percentage and display it in both formats. For our example, the superelevation is calculated as 0.057 or 5.7% as shown below:
Step 3: Check the superelevation limits
The superelevation should not exceed certain limits for safety and comfort reasons. The spreadsheet will compare the calculated superelevation with the following limits and display a message accordingly:
Maximum superelevation (emax) = 14% (recommended by AASHTO)
Minimum superelevation (emin) = 0% (for level curves)
Average superelevation (eavg) = (emax + emin) / 2 = 7%
If the calculated superelevation is within the limits, the message will say "OK". If it is above or below the limits, the message will say "Too high" or "Too low" respectively. For our example, the calculated superelevation is within the limits and the message says "OK" as shown below:
Step 4: Adjust the superelevation if needed
If the calculated superelevation is not within the limits, you may need to adjust it by changing some of the input data. For example, you can increase or decrease the design speed, the coefficient of friction, or the radius of curve until you get a suitable superelevation value. You can also change the lane width or number of lanes if they affect the cross-section geometry.
You can use trial and error method or use solver 04f6b60f66