RAILROAD QUESTION

[Anonymous]

I have stationing from a Norfolk Southern. I was told that they base their stationing off of chords instead of using arc lengths. Is there an option in Land Development Desktop to station this way?

[Anonymous]

Hi, I would double check your information. If stationing was based solely upon chord lengths, you would have to have an equation at every PC/PT in LDT. I would think it would get quite messy - anytime you have more than one equation on an LDT alignment, things get pretty confusing pretty fast. Profiles would become non-sensible. For the little work I have done with railroads: 1) Railroad horizontal curves are often laid out by Degree of Curve, where the railroad definition is different than it is for highway design (chord definition instead of arc definition). Perhaps this is what you are referring to? If so, when laying out LDT curves by Degree of Curve, you can choose either the arc or chord definition. When inquiring LDT curve data, you can get the degree of curve by either chord or arc definition. Labeling degree of curves can be accomplished with the appropriate label equation. But, this has nothing to do directly with stationing. 2) Spirals, spirals and more spirals. The clothoid spiral, which is based upon degree of curve, is used most often for railroad design. If your stationing was based solely on a composite chord baseline, the addition of spirals to the stationing mix would complicate your LDT station equations and profiles beyond belief. You could always layout a baseline alignment composed solely of linear PI's, and station (and offset) the curve and spiral elements off of it, but I could not imagine that the curve stations would have much meaning, and your profiles would have less meaning. sc "newtoneng" wrote in message news:26046836.1100802141466.JavaMail.jive@jiveforum2.autodesk.com... > I have stationing from a Norfolk Southern. I was told that they base their stationing off of chords instead of using arc lengths. Is there an option in Land Development Desktop to station this way?

[Anonymous]

Railroad curves are stationed by 100' chords (called chord definition). So, therefore, your curve length is going to be different from the stationing. You will need to get the design plans for the railroad in order to accurately recreate the centerline. Also note that many railroad centerlines are spiral (thus the reason for the chord stationing). "newtoneng" wrote in message news:26046836.1100802141466.JavaMail.jive@jiveforum2.autodesk.com... > I have stationing from a Norfolk Southern. I was told that they base their stationing off of chords instead of using arc lengths. Is there an option in Land Development Desktop to station this way?

[Anonymous]

I don't believe this statement is correct. Railroad alignments are stationed in exactly the same way that roadway alignments are stationed. The difference is that railroad alignments and roadway alignments define the "degree of curve" differently. Roadway alignments define the degree of curve using the "arc" definition (the central angle subtended by a circular arc of 100 feet, or Dc = 100 * Delta / L), and railroad alignments define the degree of curvature using the "chord" definition (the central angle subtended by a chord of 100 feet, or Dc = 2 arc sin (50 / R) . As steve said, this has nothing to do with stationing. In both cases, stations are measured along the path of the alignment, not along 100' chords. If there existed a roadway alignment and a highway alignment that were identical (the same tangents, spirals and RADIUS curves) the stationing would be identical. The only difference would be the Dc of each curve. Jon Rizzo Langan Engineering and Environmental Services, Inc. "Dennis Hyman" wrote in message news:419d14be_3@newsprd01... > Railroad curves are stationed by 100' chords (called chord definition). So, > therefore, your curve length is going to be different from the stationing. > You will need to get the design plans for the railroad in order to > accurately recreate the centerline. > > Also note that many railroad centerlines are spiral (thus the reason for the > chord stationing). > > > "newtoneng" wrote in message > news:26046836.1100802141466.JavaMail.jive@jiveforum2.autodesk.com... > > I have stationing from a Norfolk Southern. I was told that they base their > stationing off of chords instead of using arc lengths. Is there an option in > Land Development Desktop to station this way? > >

[Anonymous]

Not to be arguementative, but being that I'm just a lowly draftsman, I did have this verified through two registered land surveyors here in the office. Both stated that railroad stationing along curves was based 100' chords, and that the actual arc length between stations would actually be longer. The reason for this being done is because railroad curves are spiral, and are very difficult to define in the field. It's much easier to lay out by chord definition. Either way, the best thing to do is to get the railroad design plans, and verify for yourself. I've personally tried to produce a centerline curve on a railroad, and never have had the curve stations match the description. Only with the plans can you accurately place the centerline, with the tangent in, tangent out, and the spiral information. "Jon Rizzo" wrote in message news:419e028a$1_3@newsprd01... > > I don't believe this statement is correct. Railroad alignments are > stationed in exactly the same way that roadway alignments are stationed. > The difference is that railroad alignments and roadway alignments define the > "degree of curve" differently. Roadway alignments define the degree of > curve using the "arc" definition (the central angle subtended by a circular > arc of 100 feet, or Dc = 100 * Delta / L), and railroad alignments define > the degree of curvature using the "chord" definition (the central angle > subtended by a chord of 100 feet, or Dc = 2 arc sin (50 / R) . > > As steve said, this has nothing to do with stationing. In both cases, > stations are measured along the path of the alignment, not along 100' > chords. If there existed a roadway alignment and a highway alignment that > were identical (the same tangents, spirals and RADIUS curves) the stationing > would be identical. The only difference would be the Dc of each curve. > > Jon Rizzo > Langan Engineering and Environmental Services, Inc. > > > > "Dennis Hyman" wrote in message > news:419d14be_3@newsprd01... > > Railroad curves are stationed by 100' chords (called chord definition). > So, > > therefore, your curve length is going to be different from the stationing. > > You will need to get the design plans for the railroad in order to > > accurately recreate the centerline. > > > > Also note that many railroad centerlines are spiral (thus the reason for > the > > chord stationing). > > > > > > "newtoneng" wrote in message > > news:26046836.1100802141466.JavaMail.jive@jiveforum2.autodesk.com... > > > I have stationing from a Norfolk Southern. I was told that they base > their > > stationing off of chords instead of using arc lengths. Is there an option > in > > Land Development Desktop to station this way? > > > > > >

[Anonymous]

"Dennis Hyman" wrote in message news:41a1ec1e_3@newsprd01... > Not to be arguementative, but being that I'm just a lowly draftsman, .... Not only that, but you're 100% correct. I've been told that the old survey chains (remember when most railroads were built) were 100'. Set an instrument at a point, zero to your backsight, turn your degree of curve and put the end of the tape on line. Works quite nicely for that purpose. I'd be surprised if Land does not have a setting for this. If not, it certainly should. Chord defined arcs are quite common. I've even some PennDOT rights-of-way defined with them (pre-1950s, I think). Then again..........hehehehe

[Anonymous]

FYI - some rail transit agencies use the arc definition for their curves (ex. San Diego) - it depends upon the owner of the railroad.

[CoryHallisey]

I'm here for that very same reason.  I need to recreate a baseline that was originally created with chord definition stationing.  Creating the curves is not a problem, but getting C3D to station them correctly seems to be impossible.