Road Profile - Vertical Curves 2

[racv2]

Knowing the location (station) and elevation of my High and Low Points on the centerline of a road, how can I calculate the station and elevation of PVI. The desired curve length is 50'.

 

[jeremyk55]

The most straight forward approach is to set up the vertical curve equations (green book chap 3) in a spreadsheet. Figure out what your constraints are (entrance grade, exit grade). Modify the other variables until you get the desired low/high point. Depending on how many variables you can change, you may have multiple solutions. Are you tieing into an existing alignment adjacent to your curve or can you choose the entrance and exit grades?

 

[racv2]

Hi jeremyk55,
Yes, I can choose the entrance and exit grades.
Thanks for responding.

Do you know where can get the spreadsheet with the vertical curve equations?

 

[jeremyk55]

For a problem like that, I would start with an empty Excel file. You can then input the equations manually. As an alternative, if you have design software such as inroads, you can find a graphical solution by moving the PI until the low/high point hits your station/elevation. Even if you don't have inroads, you can place parabolic curves with cadd software, however you probably won't be able to determine the low/high point accurately.

 

[proletariat]

It sounds like you are looking for the equations themselves. If you don't have a copy of the green book, and don't want to buy one, look on the web for design manuals from your state DOT. These are usually free publications which are downloadable and have the vertical curve equations regurgitated within the text somewhere.

 

[LCruiser]

It's just a parabolic curve for constant g through it.

 

[Hoagie]

Any first year surveying or highway design text book has the equations. You should be able to find the equations online, also.

Be careful RacV2, there are other variables to a proper vertical curve design (i.e. K-value, stop/sight/headlight distances, max gradebreaks between tangents, etc.).

Good luck,

H.

 

[proletariat]

Also... The minimum curve length per AASHTO is 3 x the design speed in MPH.