How can I plot the parabolic curve for LOS F?

I have plotted the graph of Avg. Spot Speed (Y-Axis) Vs. Volume/Capacity Ratio (X-axis)  and the curve seems to be parabolic till V/C=1 but below V/C less than 1 it doesn't come parabolic so how...

05 February 2015 8,520 3 View