In this case, you are only translating or sliding the departing tangent line (-2%) to the left, while the PVC and starting tangent line (4%) remain fixed in place. As the departing line is moving toward the left, the PVI where the two lines intersect is moving to the left but also down relative to the original PVI location, thus lowering the parabolic curve.When i calculated i got the same numbers as you. However, after looking into it more, it seems as if the tangent will be raised 1.59m not lowered? I found that that the original distance from the tangent to the curve is 28.5m and the distance using a 897m curve is 26.91m which means the curve has moved up. I found that the max clearance is using 4% and -2% was using a curve length of 993.33m. Which lowers the tangent by 1.3m and the clearance over the tracks is 7.255.
Shortening the curve more will result in the tangent to move up and the clearance to move closer to 7. But i need to have 1.3m of clearance, so i found that the closest i can get to 7m and still have at least 1.3m of clearance is using a 993.33m curve.
Are these assumptions correct?
Thanks!
You actually increased the vertical clearance to 7.255 m because of the longer vertical curve length rather than decrease the clearance to 7 m to solve for the maximum reduction in curve length.Alright ya that makes sense now.
What i did was find the distance from the PVT to the approaching tangent using: Y=((g2-g1)/2L)*(x)^2= -28.5m. Than i subtracted another 1.3m, so -28.5-1.3=-29.8
Than solving -29.8=((g2-g1)/2L)*(L)^2 for L I got 993.33m. Than found the elevation 281m from the PVC, which came out to be 278.955m
278.955-1.4-270.3=7.255m which provides enough clearance.
But i see now where i went wrong.
Thanks a lot for your help!
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