Why are railroad curves amount of curvature given in degrees? How is this angle determined?
Curvature is degrees of change of direction per 100 feet of arc. So if you travel 100 feet and you aimed at a point 2 degrees different from where you started, you are in a 2 degere curve.
Radius? …Railroads don’t need no stinkin radius!!!
And oltmannd, if you took a quiz on railroad engineering/ surveying, you just FLUNKED. Try 100 feet of chord (Military 100’ chord definition)…Highway rubber tired engineers and land butchers (land development surveyors and lawyers) use the 100 Ft. arc definition.
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[:D]Indeed. And you would be surprised (or maybe you wouldn’t[}:)]?) how many land surveyors/highwaymen (oops… highway engineers[:I]) and sundry other folk who should know the difference don’t. Drives me nuts.[banghead]!
A long time ago I came across a book that described how the track gang laid a railroad curve.
First, they laid a 100 foot tangent.
Then looking in a book of tables that listed off sets for the the various degrees, they used the information and placed stakes at the 50 foot and 100 foot locations as specified by the table.
Easements could be made during the first several 100 foot tangents.
My 1950 era slide rule had sine and tangent scales on them, but for angles less than 5 degrees, they were combined on the same scale as they were nearly equal.
Chords and arcs for angles less than 5 degrees are, for all practical purposes, equal.
Art
Who knew? I’ll just go stand in the corner for a while…'till you feel better.
(and on a 2 deg curve the difference is what, 0.005%? R= 2864.79’ vs 2864.93’)
…How could oltmannd flunk if the two figures are that close…! Maybe no need to stand in the corner. It is an interesting subject.
JCHNHTFD and I will try to take the high ground here…The longer the curve gets or the sharper the degree of curvature gets, the greater the lateral displacement. On long curves, those lateral throws can amount to multiples of feet. As one who teaches railroad surveying and engineering fundamentals, it still amazes me how ignorant some engineers/architects/surveyors can be. Have had two cases here in Denver where foundations for major structures have had to be torn out and re-poured becaused the building encroached on the railroad because somebody guessed arc definition for a curve and blundered. Part of my livlihood is funded by cleaning up blunders made by others and “getting it right”. (It goes the other way too, have gotten involved in cases where BNSF and UP have built track off their R/W and are suddenly redfaced about having to buy extra ground.!) Professional Engineers are supposed to not be guessing on these things and operating within the limits of their expertise. Find gaps and overlaps all the time created by people guessing (and then there are the clowns that think you can have parallel spirals, do three point on the curve solutions in the middle of spiral curved track or back into a railroad boundary)…The intent from this railroader is to teach and not to castigate. Oltmanmd needs to come out of the corner and learn (got his attention I hope, he can join me in the corner for other transgressions -nobody is perfect here.)…It might not be that big a deal to shift a r/w line out in a cornfield, but it gets expensive in a built-up urban area where land goes for up to $100 per square inch. Can also think of multiple cases where new buildings got pieces or corners cut off because they were on the wrong side of a line.
To answer another part of the original question, in the days before calculators, laying out curves or figuring curve equations with radii in the equation was a major pain in the tush. Give me degree of curve and a delta and I’m gone (and probably finished) before the
I think the lesson is, if you make that small error a couple of times over the course of 20 miles, you will notice.[;)]
A hundred feet of chord seems much easier for me to understand than a hundred feet of arc because it is a straight line measurement to a point of arrival. It’s been a while since I had basic geometry, but a hundred feet of arc should give a chord something less than a hundred feet right? Although, oltmand is probably right in such a broad curve the diference must be very small, but such diferences can add up over a great distance. At any rate engineers measure twice right?
It’s a good thing navigators don’t use radius. In navigation, it is common to divide a great curve into a series of chords.
The rationale of a military engineer…congrats![8D]
Oh my! I am speechless…
I am having trouble getting my fingers around this, but if this goes through a group of people - architects and engineers and no one catches the mistake until Mark’s sample up above - then who pays for the “adjustments”? And does this type of thing happen very often (probably more than MC would like)? I know it happened here on a highway.
Mookie
Mark
I don’t want to second-guess here, but I have one question. No surveyor or Project supervisor thought to check and verify that the two towers were being constructed on the same datum? I find that hard to believe, since (I assume) that they should have been within a single-turn level circuit of each other. That’s one of the first things we do, even on simple highway and bike path jobs.
MC
Do you have a favorite source for those cord offsets for laying out curves? I can’t count how many times I have been asked in the field to move this turnout ahead 115 feet so that they can build it in place without taking the track out of service or cutting off the ends of the ties and “move and adjust the curve so that it still lines up at the other end”. Or my next favorite, “somebody designed this cross-over on 13 foot centers, can you spread it to 14 foot?” (in a curve, naturally).[banghead][banghead][banghead]
…“And does this type of thing happen very often”…Jen, I went to school with a buddy and his dad started a construction Co. many years ago and some years ago “Mike” told me of a mistake on an interstate I’ve been traveling for about 40 years…That is the tunnel at Wheeling, Wv. on I-70…He indicated there was an elevation mistake of 4 ft. made there during it’s construction…I’ve noticed an unusual dip at it’s approach for years but don’t know if that is what he was referring to or not…Perhaps if the story is true it was modified in some way to allow construction to be completed, etc…I’d guess we “drive” over many “errors” in our daily routines.
Whatever COGO package is appropriate for office or field…no two solutions are ever the same…Who do you shoot first…the designer, the track foreman or the roadmaster when they ask you that question??? Mysteriously they never are around when everybody starts complaining when everything around that relocated switch does not work as intended.
It is a real shame that HP quit producing the HP-48GX, the TDS card that goes with that thing can really dance. The HP Marketing People (morons) seem to think everybody uses a laptop or an office CPU & monitor and nothing else. When you have to work in the field and design on the fly, even the smallest laptop is an anchor and chain wrapped around your neck. The remaining handheld calculators on the market all all garbage and cannot be used as a data collector very well, if at all.
[}:)][}:)][}:)] My favorite sore point is the track foreman that is too lazy to saw a rail at the appropriate place, so he “heels-in” the toe of frog for a turnout, screws-up the track allignment and then howls that nothing fits (and it could not be that he moved the whole turnout and switch assembly 10-35 feet down the line .
Switches/ Crosovers in curves? - SHAME! SHAME! SHAME![V][V][V]
Mookie – I wasn’t going to start on horror stories, but… there is a location in northern New England where the surveyors going south were lining the southbound barrel of an interstate up on a certain centre line, and the surveyors going north were lining the northbound barrel up… on the same centre line… there is a nice ‘S’ curve in the interstate there now. You can’t do that sort of thing on a railroad, and in my humble opinion the guys (both office and field, but particularly field) who do railroad work are a completely different class of engineer and surveyor. Definetly superior (not to say they don’t make msiteaks from time to time – just that they seem to be more careful).
That HP48GX was a wonderful calculator… I had a several nice little routines which I could plug into my HP33 which did offsets and another for spirals and another for vertical curves, too. It died, long ago. The calculator, not the program.
Q - I am sure this probably does happen every day - but on a big scale like that! That is something that just doesn’t make the paper every day, either.
Our highway was so obvious, it became the joke of Lincoln! There was a definite jog in the road and it is wide highway - turn lanes and all. They corrected it, but still not too sure who ended up footing the bill. Probably don’t want to know.
Fascinating!
J
The farther you get away from the “nuts and bolt” end of railroading and the closer you get to marketing, the less significant digits you have to bother with! (operations is about 1/2 way in between)
But marketing of all people should be very concerned with the significant digits - since the end product will be used in future “sales”…or am I missing something again!
Would see to me that you want your project to reflect what a good job looks like - and the devil is always in the details!
Yeah - you are right from that point, but would seem to me that say in Mudchickens world - you find out that a company muffed it with figures and had to redo a major project - that would be predicting their behavior in the past and the future?
I guess I just can’t get past the Oops I muffed it on something that big and just brushing it off as oh well, things happen.
Yeah, you are right - I do live in a very small world!