elevation of tracks at Rural Retreat VA

[NW Mailing List]

Early surveys, in general, were quite interesting. The ones that were done by first-rate survey crews (French and British gov’t supported) were astoundingly accurate. For example, in the 1790’s, Fance and Britain, in a brief period of cooperation (one that was intended to get to a common unit of measure, to be based on the “second’s pendulum - one the US was also trying to implement), measured the distance between London and Paris. That measurement, done with finely crafted mechanical instruments, was within twelve feet of today’s measurement. 

That cooperation, which included proposals to decimalize weights and measures (and even time!) fell by the wayside when the French arbitrarily decided to use a sub-unit of the meridian passing through Paris as their base unit of measure, with the argument that a “second” was too arbitrary to base a unit of measure on…

Closer to Abe’s topic, the chain used in chaining was developed in the 1600’s - called Gunter’s Chain. An ingenious device that was able to rationalize traditional measures (acres, perches, human "day works") and an early decimalization (100 links on the chain). It was also simple enough that a below-average survey crew could get reasonably good results - though not to the accuracy noted above, for lack of very expensive equipment and lack of ability to understand the math involved.

The above from a fine book called “Measuring America” by Andro Linklater. 

Matt Goodman

> On Jun 6, 2025, at 9:31 AM, NW Mailing List <nw-mailing-list at nwhs.org> wrote:
> 
> I would not get too firmly wedded to those elevation numbers on N&W and NS track charts.  Here's why...
> 
> Back in the late 1980s, I was at an industry meeting where various issues affecting all the railroads were being discussed.  Someone from the Union Pacific stated that his company had come to question the vertical elevation data in its engineering files.  Most of their chain-survey numbers were from around 1900, and some of them went back to the original surveys for the Transcontinental Railroad in the 1860s.  Discrepancies abounded between the original elevations taken, and those made with more modern instrumentation and techniques. It was found that in one place the modern, accurate elevations differed by as almost 90 feet from the 1860s surveys.  A portion of this inconsistency was probably due to inaccuracies of the original survey parties, but it was believed that subsidence of the land contributed to the discrepancy, perhaps occasioned by subsidence due to pumping of the aquifers, and to crustal plate tectonics, as well.  And who knows what other forces, yet unknown, affect the lithic structures of a continent.
> 
> My guess is that the NS Chief Engineer's office still has the original leather-bound surveyors' notebooks from the earliest chain surveys, for lines they have not sold off.  If you ever get the chance to look at one of those field survey books, do it!  They are works of art, and were always recorded with a very sharp pencil.  One I happen to have begins with this notation inside the front cover, "Survey of the Columbia & Port Deposit Railroad, Begun March 28, 1900, 10:40 AM, at a bronze bold driven in the north backwall of the Susquehanna River Bridge at Perryville, Md, weather 52 degrees, Clear.  Party:  (stick drawing of a little tripod, indicating the instrument man) J B Schmidt, (stick drawing of a surveyor's chain, indicating the chainmen) F. Fierman and M. Blickensderfer, (stick drawing of a little book, indicating the man who recorded the data in the notebook) N. Metzger.  Chained on the north rail beginning at station 0+00."  All field notebook records were expressed to the tenth of a foot.  Things noted were OH wire crossings and bridges, UG bridges, pipe and culvert crossings, bridge backwalls, PS point of switch, PF point of frog, PT point of tangent, PC point of curvature, PCC point of compound curvature, the exact location of every sign and signal, exact measurements of every structure, &c.  It was from  such survey records that the Valuation Maps were drawn.
> 
> Another fly in the ointment of accuracy pertains to the track chart entries showing footage between Mile Posts.  Almost never is 5280 feet shown between MP's... even in the early field survey notebooks!  Sometimes the footage is over a mile, sometimes it is under, and the discrepancies can be tens of feet, or in a few cases, several hundred feet.   Why?  Had some Mile Posts relocated?  Did lateral realignment  to the track structure lengthen or shorten the footage between Mile Posts?  Was the footage data of the track charts ever re-calibrated by fresh survey data (I doubt that !)  
> 
> Now, let's bring this little discussion up to modern times.  About  25 years ago I was handed the job of working with a railroad project of the Pennsylvania State University's Civil Engineering Department.  My assignment was simple -- "Get them whatever they need."   Their study involved measurement of the propagation and amplitude of the sounds made by an approaching train through the steel rails. They used one of our 40 MPH branches as the test bed for their experiments and measurements, and as I recall, we gave them an engine and a crew for a week, on more than one occasion.
> 
> During those test runs, I asked one of the project engineers about the accuracy of the vertical and lateral GPS coordinates they were using (all satellite based.)  I must rely on memory for the conversation, but as I recall, the accuracy of the coordinates and elevations was stated to be "within Centimeters."  And that was 25 years ago, before the advent of using drones and RTK (real time kinetic update) for survey work !
> 
> So, if you want exact measurements for the surface of the grade crossing at Rural Retreat, use the Global Positioning measurements made by triangulation of satellite signals... not 125 year old railroad records which were probably "good enough" when made, but not highly accurate.
> 
> Recalling the words of the ancient Greek philosopher, Heraclitus,"You cannot step into the same river twice.  Panta rei (everything flows.)"
> 
> -- abram burnett
> (T squared X 1) / 1 = Turnips
> 
> 
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