RR Spiral Curve Help

Where they all started.  The rail road. Don’t know if this will help but remember the difference in regular curve and rail road degree of curvature. Also make sure the distance between stations is not along the arc it’s a tang distance. Sometimes with RR the math doesn’t do it justice. Might have to just locate what’s physically there and gain some understanding of what was supposed to be. 

Was it Loyal Olson who was our expert on spirals?

For circular curves I made a program that deals with both RR and hiway curve definitions. The link in this thread may still be good.

https://rpls.com/forums/strictly-surveying/messin-with-horizontal-curves/

I'm not a railroad expert -- fortunately, in my area most them run straight as an arrow for miles (my local depot notwithstanding, it's at a 3-way interchange).  However, I recall reading that, at least for some railroads, the ROW was created using circular curves, even though the centerline was built on spirals.  So the historical research is at least as important as the calculations.

No RR expert here either but my software put the data you posted together and it looks good. The first station 445+18.4 appears to be NFG if we hold the other 3. I hope this helps and it would be really nice if somebody else would check my work.

As Jim said above almost all older RR right of ways were taken as simple curves. Not all, but mostly that's how it was done. Then maps (Val maps) were issued that were concentrating on tax value and showed the tracks which were more important than the exact ROW location and of course the tracks will be SCS. So, there can be a disconnect using Val maps. I've gotten good luck with our newer clearinghouse for ROW plans, so far none of the maps they've sent me show any SCS on the right of way and they are more modern and comprehensive for deed research than the older ones. The old RR original maps can sometimes be found in the national Archives in Virgina. You can research the RR online, it can be frustrating but it's possible.

Good luck with your project, research is the most important first step.

AutoCad does a very good job using alignments to create the SCS.

One thing to consider and it's a vexing issue; if you go far enough along an east-west line you really need to consider convergence. That's been helpful retracing old RR and highway right of ways for me. Check the real bearings on the physical track centerline and expect it to converge over any longer distance. 

The radius for the above example is very tight for a RR curve. A more urban area or difficult topography?

One aside about RR info, if it isn't an even or 1/2 degree of curve it's probably not the original described curve. You have a 10d curve and try it as SCS and simple curve using the tangents. That probably won't make much of a difference and possibly a simple curve solution may fit evidence better. And pay very close attention to any reference of a found ROW monument on the plans you have. Those are gold.

Posted by: @mightymoe

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Then maps (Val maps) were issued that were concentrating on tax value and showed the tracks which were more important than the exact ROW location and of course the tracks will be SCS. So, there can be a disconnect using Val maps.

Was at a continuing education seminar put on by a surveyor from CSX years ago. He started out asking for people to raise their hands if they relied on valuation maps to retrace railroad rights-of-way. After about 80% of the class raised their hands, he said (paraphrasing) "interesting... I would think that after all the hard work to get your license you would be averse to playing Russia roulette with it.  Always get the deed that created the ROW or transferred the fee"

Posted by: @james-fleming

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Always get the deed that created the ROW or transferred the fee"

Deeds are an interesting subject in some areas. The RR locally is shown as granted on GLO records in the 1880's to 1890. But they didn't define the RR widths because I guess it was unpatented lands. Then Val maps were produced, then patents were issued along the existing Railroad. Probably it occured to someone that the patents didn't reference the Railroad and were overgranted by the area contained by the railroad in the patent. Then deeds were written for the railroad 30-50 years after it's already been constructed and in longtime use. But, the deeds don't really match with evidence of the RR the val maps ect. We've found a number of original ROW monuments and section corner ties that all match, but don't come close to the "deeds". 

Some of those deeds are wild, I have an area where they change width by the time of year. 

Thank you all very much for the input, placing the ROW is a whole other problem. This particular one goes up a long winding canyon, was abandoned, the tracks removed and a freeway now resides where the tracks once were. The difficulty is that the abandoned ROW was deeded to the department of transportation and the Railroad ROW comes and goes within the road ROW. In this area many of the ROWs are defined with spiral curves. 

I really appreciate the time you put into solving the example question Landbutcher. It is evident that this isn't a clothoid spiral and i was able to solve how this one was put together based on the information you provided. The only thing that still perplexes me is the "Radius" of 584.42 feet along the spiral. I cant figure out where the radius comes from, much less how to calculate it

I wrote an excel program to solve spiral curves, with the option to “force fit” the spiral to match TS and SC stationings. Particularly with old railroad spirals, which were often pulled from tables, in the pre-calculator days. The problem is every curve adds a little bit of error, so after 20 curves, your stationing can be off by a foot or 2. You can either adjust the spiral by a few seconds to correct, or add a station equation to your survey. 

happy to share the excel program, feel free to message me directly.

When I moved from fieldwork to the office I was doing some research at the local department of transportation office when the elderly surveyor in charge told me a valuable lesson. Put yourself in the shoes of the of, or a close as possible, to the original engineer or surveyor doing the calculations. They probably didn't have a computer or calculator which read to the significant figures we can determine now, but were using values shown from books with tables in them (Searles comes to mind). So, looking at the date of the original calculations, I would consult our archives to find a the railroad design book which matched closest to the date design. This method seemed to match closer with asbuilt maps and field ties of the rails.

@sbrak "The only thing that still perplexes me is the "Radius" of 584.42 feet along the spiral. I cant figure out where the radius comes from, much less how to calculate it."

Again I am no expert on spirals and I misled you with my last sketch. According to Google that 584.42' radius should have been the same as the circular curve radius of 572.94' so there is some error in my software or I probably fed it something incorrectly. The spiral radius is infinity at 445+65 and transitions to 572.94' at 447+18. There must be a formula for calculating the spiral radius at any point along the curve but I did not look for it.

I did find this spiral calculation guide and it goes thru calculating an example spiral and I attached a revised sketch.