The centerline of the railroad defines the location of the centerline of the adjacent highway. Without getting into a lot of hypothetical questions about whether the railroad centerline or the railroad ROW fences are in the correct location (let's assume they are), is the common ROW line defined as chord definition or arc definition? The railroad centerline is defined as chord definition. Also, assume there are no spirals on the railroad involved. The extension of the radius lines from the railroad curve's P.I. defines the beginning and ending of all five curves. Using the same delta for both the railroad and highway centerlines, I believe the highway centerline should be defined as arc definition as should the outside ROW line of the highway, but what about the common ROW line? The railroad was there first and the highway parallels the railroad. Curve data needs to be shown for all curves on the plat. Is there a precedence for this?
I would say the ROW line between the two would be an arc. It wouldn't matter how you described it as long as it is the same arc.
James
I do have one of those, I used the cord definition, it was referenced in the ROW taking as 50' north of the north RR right of way, I kept it a chord through the highway also.
Why?
As I see it, the only way this would affect the labeling of the curves is if you include the degree of curvature. I always list the radius, arc length, ch bearing, ch distance. That way, railroad vs. highway definition shouldn't matter. Interesting question though.
You could label it both ways: Da and Dc. These are used as standard abbreviations in both Elementary Surveying (Wolf and Brinker) and Surveying Theory and Practice (Anderson and Mikhail). (They're written as D sub a and D sub c, but couldn't show that here with the limited text options.)
[USER=10394]@The KGB[/USER]
Simple, isn't it?
I'm not a layout guy, perhaps including degree of curvature would make more sense if I were. Give me a radius and delta or a radius and stationing and I'm a happy camper. An incoming and outgoing radial would be nice if things weren't tangent.
The KGB, post: 438446, member: 10394 wrote: As I see it, the only way this would affect the labeling of the curves is if you include the degree of curvature. I always list the radius, arc length, ch bearing, ch distance. That way, railroad vs. highway definition shouldn't matter. Interesting question though.
Holy Cow, post: 438453, member: 50 wrote: [USER=10394]@The KGB[/USER]
Simple, isn't it?
As the best practice, I agree with you guys. KGB's elements contain everything you need. I think they're BLM's standard elements as well these days.
I see your dilemma Jerry.
ASSUMING that the Railroad & Highway Documents use the [exact] same delta for the two centerline curves, AND the Highway Curve is Stationed using the ARC definition AND a radius derived by ADDING ?« of the Railroad ROW [width] + ?« of the Highway ROW [width] to the RADIUS of the Railroad Curve, "they are going to get a DIFFERENT "length" of Curve than one would using the CHORD Definition [length]. This COULD end up with some screwy stationing relative to the Highway Documents. Railroad Curves are always (at least round these parts) defined by DEGREE of CURVE (Chord Definition), and generally so are Highway Curves (which might use EITHER ARC or CHORD Definition).
So...IT DEPENDS (on what the highway boys "did")
Fun and games.
Loyal
I would say it depends on how the road was stationed. The only difference between the two definitions is the arc length and the degree of curve. Since the only thing I ever see with degree of curve anymore are rail plans that leaves you with the arc length. If you are trying to station the road then you will want to use the arc definition. If you are not worried about stationing then it really does not matter as long as you label it. As for the curve info, all you really need to show is the radius and included angle, the rest is just a check. You could also label the lines with both arc and chord lengths.
If the railway was established followed by the road, the degree of curve methed for the rr will control. Early curves were Dc and the angle was usually tied to common instruments and easy numbers.
Randomly assigning different methods changes the radius. In some cases its trivial, usually not.
An arc is an arc, a chord defined arc can be described as a simple arc. The same arc curve would have a different length in each system.
I do not quite see what your problem is.
Paul in PA
Paul in PA, post: 438495, member: 236 wrote: An arc is an arc, a chord defined arc can be described as a simple arc. The same arc curve would have a different length in each system.
I do not quite see what your problem is.
Paul in PA
One word Paul:
STATIONING!
Railroad Stationing (even on "flat ground") will return DIFFERENT PC & PT STATIONS than the SAME Curve will using an ARC Length to determine said Station values. This isn't a big deal, so long as everybody is on the same page. I have seen quite a few HIGHWAY Projects that used Chord Definition Curves (Degree) but ARC Length Stationing.
Loyal
Loyal, post: 438496, member: 228 wrote: I have seen quite a few HIGHWAY Projects that used Chord Definition Curves (Degree) but ARC Length Stationing.
Loyal
[SARCASM]The person that decided that must have also come up with modified SPCs jacked up to an "average" ground elevation.[/SARCASM]
J. Penry, post: 438432, member: 321 wrote: The centerline of the railroad defines the location of the centerline of the adjacent highway. Without getting into a lot of hypothetical questions about whether the railroad centerline or the railroad ROW fences are in the correct location (let's assume they are), is the common ROW line defined as chord definition or arc definition? The railroad centerline is defined as chord definition. Also, assume there are no spirals on the railroad involved. The extension of the radius lines from the railroad curve's P.I. defines the beginning and ending of all five curves. Using the same delta for both the railroad and highway centerlines, I believe the highway centerline should be defined as arc definition as should the outside ROW line of the highway, but what about the common ROW line? The railroad was there first and the highway parallels the railroad. Curve data needs to be shown for all curves on the plat. Is there a precedence for this?
About 4 years ago I sat in a RR Surveying class at the Kentucky (KAPS) conference, he was a CSX guy. A question similar to this came up and we were told that RR ROW will typically follow the Arc definition - Chord will only apply to the rails (CL).
Loyal, post: 438496, member: 228 wrote: One word Paul:
STATIONING!
Railroad Stationing (even on "flat ground") will return DIFFERENT PC & PT STATIONS than the SAME Curve will using an ARC Length to determine said Station values. This isn't a big deal, so long as everybody is on the same page. I have seen quite a few HIGHWAY Projects that used Chord Definition Curves (Degree) but ARC Length Stationing.
Loyal
Stationing will differ greatly because stationing is typically referred to as a centerline station and offset and the centerlines are described differently. If it is necessary for right of way descriptions then a lot of equations are involved. Which would get more confusing if there are also correction equations.
Paul in PA
Most of the time, the RR was there first and what ever was used for that r/w is used.
That would probably be a certain distance from the center line of the tracts.
Run a best fit situation using different points along the tracts and see what fits with the planed figures.
The other r/w of the highway is not necessarily a match and may be defined differently.
RR maybe built by chord, but according from many officials I've ever spoken with from the RR themselves and other teachings, boundary/ROW retracement is defined by arc. Looks like you've got a few more factors as well, though.
I'm not following any logic that presents the given "problem." The curve/chord definition only applies to the centerline of the railroad. The railroad would typically be defined as an even number of Degree of Curve. The rights of way are offsets of the centerline which are reported by their radius, length, etc. The Dc is an irrelevant number at that point. Offsetting the railroad centerline to the highway centerline results in another oddball Dc which is also irrelevant but could be reported by highway (arc) definition. The stationing along the highway centerline should by by highway definition. Because the Dc is irregular, I wouldn't report it. Just stick with radius, delta, length and any other necessary data.
