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Looking for help understanding Railroad Val Maps

CDM81-FLA
(@cdm81-fla)
FNG Member

Prefacing this w/ my understanding of certain aspects of retracing railroad boundaries. GENERALLY the alignment used to control the R/W is not the alignment of the physical tracks, because GENERALLY the physical tracks are spirals through the curves and the curves on Val Maps and in original acquisition documents are simple curves. That being said, it is very common in my neck of the woods to find fences and survey monumentation within the curves being record distance from the center of the physical tracks. Looking to avoid a rabbit hole about the varying thoughts on this. 

I'm looking for clarification/opinions/thoughts on this specific item:

The Val Map I'm following (and others I've seen) use the following acronyms for PC. "VPCR" & "VPCL" at point of curvature and uses exclusively VPT at point of tangency. I can deduce that the "L" or "R" at the end means left or right, as it matches the map/direction of stationing. I can't make sense of the "V". Most info I've found relates to vertical curves, but stating this on the Val Map makes no sense, as there's no other information to accompany a vertical curve. I've attached a screenshot which shows two individual curves. Any railroad experts out there, please help a guy out!

Thanks in advance!

-CDM

 

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Topic starter Posted : July 3, 2022 10:37 am
Norm Miller
(@norm)
1,000+ posts Member

1- I'm not an expert but I have played a RR surveyor at different times in my career- you get what you pay for.

2- The V may designate that the curve was designed for a standard velocity (speed)

The only reason I say that is because V is for the designated speed used in the formula for computing railroad curves according to some RR curve manuals.

Another possibility is variable due to all the forces in play. I've done a fair amount of retracing railroad curves. I was taught to set up on the central part of the curve and measure out 100 ft chords turning deflection angles through the central and transitional curves and compute something that would fit. Usually trying to hold a even degree or half degree and some sort of normal transition length. But it's kind of like surveying a stream bed - it's always on the move so it's only good on the date of the survey.

The good thing about railroad ROW is that its hard to argue against whatever evidence is chosen provided the result is reasonable. You're right that standard practice is to use the CL trk for ROW offset given there is nothing noteworthy already present on it. I've found that railroads have a habit of setting something notable on the ROW at property line intersects and whatnot. Hard to argue with that. Even harder to argue against it. 

This post was modified 1 month ago by Norm Miller
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Posted : July 4, 2022 8:18 am
CDM81-FLA liked
Brad Ott
(@brad-ott)
5,000+ posts Supporter

Valuation PC?

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Posted : July 4, 2022 8:25 am

Kevin Hines
(@kevin-hines)
500+ posts Member

Val maps are dimensioned using slope distances instead of horizontal distances, so the VPC would be the vertical point of curvature.  The railroads used slope distances instead of horizontal distances because they were taxed based on the length of track they possessed and/or operated. It doesn't make much of a difference on the flat plains, but when in the mountainous regions, the difference is substantial.

Since the primary purpose of the VAL Map was for taxation purposes, they didn't need to include the elevation differences, only the length of the vertical curves.  To recreate those vertical curves, you would need the construction plans that specified the grade entering the curve, the grade exiting the curve, and the grade at the VPI. Depending on the RR company you are dealing with, trying to get any additional information will be harder than pulling hen's teeth.

I hope this helped.  Good luck!

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Posted : July 4, 2022 10:07 am
Brad Ott liked
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