# Vertical curve problem



## utilityeng (Oct 14, 2017)

What am I doing wrong here? The answer I get is 25.75 ft.


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## DoctorWho-PE (Oct 14, 2017)

NOTE:  I am not a transpo engineer, and have a very tentative grasp of curves.  But aren't vertical curve stations based on projection onto an x-axis?  So I get that the elevation difference over 300 feet is 9 foot at a 3% grade, thus 365.94'-(334.56+9)=22.38'.  I don't know if that is correct or not.  (It would be great if it is, since I didn't look that up at all.)


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## ExhibitGuy (Oct 14, 2017)

utilityeng said:


> What am I doing wrong here? The answer I get is 25.75 ft.


Everything looks good, except you accidentally forgot about the double negatives in calculating your R value. The R value should be +0.3333% . Using that R value i get an answer of 19 ft (B) (anyone else able to confirm?)



vhab49 said:


> So I get that the elevation difference over 300 feet is 9 foot at a 3% grade, thus 365.94'-(334.56+9)=22.38'.  I don't know if that is correct or not.  (It would be great if it is, since I didn't look that up at all.)


That would be correct, but the elevation difference you calculated is between the structure and a _projected line from the beginning of the curve._ You want to calculate the elevation difference between the structure and the curve itself.


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## utilityeng (Oct 14, 2017)

Thx for the reply vhab. I stumbled upon a thread that supposedly shows the answer as 19', but the equations used are not the same as those in the current version of the CERM, so not entirely sure how it all relates to the equations I used.


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## utilityeng (Oct 14, 2017)

ExhibitGuy said:


> Everything looks good, except you accidentally forgot about the double negatives in calculating your R value. The R value should be +0.3333% . Using that R value i get an answer of 19 ft (B) (anyone else able to confirm?)
> 
> That would be correct, but the elevation difference you calculated is between the structure and a _projected line from the beginning of the curve._ You want to calculate the elevation difference between the structure and the curve itself.


Dang it Exhibitguy, I think you nailed it. It's little mistakes like this that are gonna cook my goose come October 27th. Thx for catching my error!


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## ptatohed (Oct 15, 2017)

I get answer B as well.


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## DoctorWho-PE (Oct 16, 2017)

utilityeng said:


> Dang it Exhibitguy, I think you nailed it. It's little mistakes like this that are gonna cook my goose come October 27th. Thx for catching my error!


I'm with you! Thankfully I should not have to encounter many of these on the test.  Good luck utilityeng.


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