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Spiral Curves Blah

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thebionicman
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Idaho roadways created by prescription can be limited to improvements or a set statutory width. The law here is not simple and few have bothered to read (much less understand) it. They simply echo the last incorrect width shown by a surveyor or asserted by a receptionist at the local highway department.

One of the Boise law offices maintains an excellent road handbook and posts it free online.


 
Posted : August 13, 2024 2:11 am
thebionicman
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I did forget you mentioned that. Have you reviewed the grantor grantee indexes at the County? If there are state plans there were almost certainly deeds.


 
Posted : August 13, 2024 2:26 am
BStrand
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...or asserted by a receptionist at the local highway department.

Well, that's not a surveyor problem, imo. If I call the agency that is supposed to know and... they don't know then... 🤷‍♂️

One of the Boise law offices maintains an excellent road handbook and posts it free online.

Do you have a link to this handy? I'm not sure if I have this in my collection.


 
Posted : August 13, 2024 2:35 am
BStrand
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I did forget you mentioned that. Have you reviewed the grantor grantee indexes at the County? If there are state plans there were almost certainly deeds.

Not yet, but I did put in an order for a title report so we'll see if anything shows up there.


 
Posted : August 13, 2024 3:20 am
thebionicman
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The link is about a paragraph long. Do a search for Givens Pursley Idaho road law handbook and it will pop up.

In the meantime a little food for thought...

We form professional opinions based on evidence evaluated under the law. Why is it acceptable to simply list the assertion of a person with no authority as our professional opinion of a right of way location? That is tantamount to asking the neighbor of our client where the boundary is and mapping it without question. The next surveyor then shows what we have on our map without research or question.

A right of way is a boundary and must be determined to the same standard of care as any other boundary line.


 
Posted : August 13, 2024 3:47 am
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BStrand
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Why is it acceptable to simply list the assertion of a person with no authority as our professional opinion of a right of way location?

I'm not sure what you're referring to. Are you talking about a survey that perpetuates the right of way location from a previous survey?

If so then I would say presumably that previous surveyor, being the professional that the state says they are, did consult an authority and that's where the right of way location came from.


 
Posted : August 13, 2024 4:06 am
thebionicman
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I find virtually no correct right of way determinations in some counties. Zero. When I contact the surveyor they either say it was shown that way by others or the road department gave the width. More often than not the creation documents and/or governing law are easily obtained.

Part of the purpose of the narrative law was to require us to obtain and cite source information for all boundaries shown on our surveys. Records of survey cannot create rights of way and are not a valid citation.


 
Posted : August 13, 2024 4:44 am
BStrand
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Well, if someone isn't doing enough research then that's a standard of care issue.

It's amusing how some of the entities responsible for knowing this stuff don't even want to answer the question.

I've called a county to inquire about a right of way only to be told to contact a city in the county instead. When I contacted the city they immediately tried to pawn me off on the county. I go BZZZZT I already talked to them and they told me to come to you. I don't care which, but one of these fools is going to give me the info I'm after !

I talked to another city about a right of way once where the guy literally told me he didn't want to give me an answer because there was too much liability involved. 🤦‍♂️🤦‍♂️


 
Posted : August 13, 2024 5:05 am
thebionicman
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Therein lies part of the problem. The entity having jurisdiction is a matter of law. Many of those entities have no idea where the width is established and believe some manager can just declare it by fiat.

In the majority of cases a width can be easily determined with a little research. Where width is not set, the commission should make an assertion (with the advice of qualified counsel) and follow up with a road validation. If not challenged that width has certainty.

My greatest issue here is the impact of an incorrectly shown r-o-w. It can take rights from one and assign them to another, allow prohibited development, or disallow where it should be fine. These things hurt people and it is our paramount duty to prevent that. We need to put an end to survey by old wives tale and push for better practice. This old dinosaur will never stop preaching this while hammering the table..


 
Posted : August 13, 2024 5:30 am
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BStrand
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We need to put an end to survey by old wives tale and push for better practice.

I don't think any surveyor is opposed to that, but when the authority doesn't know, or doesn't want to do their job, and regularly tries to pawn the decision-making off on us (pretty sure I've had an agency respond to my question with "well what do the plats/surveys say" too) then it doesn't exactly make our job any easier.

I certainly don't mind making a decision based on the fieldwork and research I've done, but in cases where that evidence isn't clear it's important to have authorities that don't give squirrelly answers.


 
Posted : August 13, 2024 5:50 am

kscott
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When faced with the mathematical impossibility of offsetting a spiral curve I resorted to the following:

Intersect the tangents and fillet a curve using the record radius. Explain what I did and why on the record of survey. This produces a retraceable line that varies very little from the “offset” lines of a spiral.

I did not come up with this on my own, but discovered it in some unrecalled resource regarding railroad spirals. I used this with success, being I was never challenged on my results.


 
Posted : August 13, 2024 6:31 am
chris-bouffard
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In all of my years researching plans and documents filed with public agencies, I have only come across three that have been helpful and put in the work to find the answers, one was a county surveyor, another an assistant county clerk and the third, a DOT engineer. All have since retired.


 
Posted : August 13, 2024 7:01 am
dmyhill
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I’m at a bit of a loss as how to handle the spiral curve though. When I’ve worked with horizontal curves in the past I get the tangents set and then list my measured chord and the record curve data between the PC and PT. How would you do the equivalent of this with a spiral?

Short answer:

Parent parcel lying North of the centerline (as defined by...) of xxx highway.

Parent parcel lying South of the centerline (as defined by ...) of xxx highway.

Done.

Make it clear where you got the centerline information from, or what centerline the description refers to. Be clear about the intended bound. Does the owner wish to subdivide at the shown centerline of the DOT plans? Do they plan to subdivide at the centerline according to the monuments? Which one is chosen is irrelevant to the subdivision of land.

Now, determining where the ROW is EXACTLY will be relevant once someone wants to build on the land, or use it for some purpose, but I am not sure what it matters for a simple subdivision. The whole idea of offsetting the ROW for this work seems to be irrelevant.

Do not put anything on your survey that you are not sure of, and if you feel you must, then explain that in your narrative.

bionic describes the horror of following a survey and the data has no metadata. Oh, you say it is 25' half-width...can you tell me why in your narrative? Oh, you single proportioned that corner...tell me why you think the original location cannot be re-established. Just tell me the how and why! A recorded survey is a message to future surveyors yet unborn...give them the whole story.


 
Posted : August 13, 2024 10:56 am
dmyhill
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Intersect the tangents and fillet a curve using the record radius. Explain what I did and why on the record of survey. This produces a retraceable line that varies very little from the “offset” lines of a spiral.

I second this approach.


 
Posted : August 13, 2024 11:00 am
GaryG
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https://www.amazon.com/Myth-about-Spiral-Curve-Offsets/dp/1493790374


 
Posted : August 13, 2024 11:19 pm

BStrand
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Now, determining where the ROW is EXACTLY will be relevant once someone wants to build on the land, or use it for some purpose, but I am not sure what it matters for a simple subdivision. The whole idea of offsetting the ROW for this work seems to be irrelevant.

The goal is to build a large commercial operation on one of these parcels. It turns out the parcel has already been split by deed and the new deed does call out of the right of way line as the boundary.

I should back up and explain-- the client apparently split the parcel by deed and then after doing this hired my employer to split the parcel (I know I know, makes zero sense). The split was so fresh that when I requested the current vesting deed for the parcel from a title company they didn't have a copy of this new deed-- which made the initial split request look perfectly reasonable.

Anyway, all I have to do now is a topo and a record of survey to set a couple missing pins. I would like to leave a gap in the topo boundary where the spiral is and put a note to the engineer that says here's the record spiral info-- knock yoself out. 😏


 
Posted : August 20, 2024 6:53 am
holy-cow
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Surely the setback requirement for structures would somewhat dull the impact of the spiral curve. I can think of a local industrial park that has 25-foot setbacks to the required chain link fences, leaving 50-foot wide strips of nothing but a need to keep it mowed.


 
Posted : August 20, 2024 7:50 am
BStrand
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Yeah, there's about 2300 feet of highway frontage on this parcel so maybe that'll give the engineer enough room to dodge it entirely.


 
Posted : August 22, 2024 12:58 am
summerprophet
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I believe a have a solution to a few different problems posted on here and have attached an Excel file that addresses a few of the issues encountered on here. 
Page 1 will calculate all the values of a spiral, and will output the mathematically precise values AS WELL AS outputting adjusted values that will slightly adjust the spiral values to match plan stationing perfectly.

The second sheet will approximate the spiral using a series of tangent curves and a small tangent line. This solves the spiral offset problem. 

A few things to note:
I don't know your state laws and licensing board requirements. In Washington state, I would label the spiral accordingly, and make it very clear that the tangent curves are an approximation. 
LS (spiral length) in Washington is usually represented in 100's of feet (200' long spiral would have a Ls of 2). Not sure about other states, but in Canada, it is represented as the actual length. 
All the Compound Curve points fall exactly on the spiral. This means any offset staking would be accurate at these points. Curve to Tangent point, and any other points would not fall exactly on the spiral, but would fall within the maximum deviation shown on sheet 2.

Best of luck,

 


 
Posted : November 10, 2025 10:40 am
Landbutcher464MHz
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Just guessing here because I have almost no experience with spirals. My software, PCSurvey, will create a spiral using any 2 of 4 variables. Then I can select that spiral and create an alignment. Then I can select begin and end points and any points between and ask for a station offset report. I get stations on all the selected points and their offset left or right from the spiral. If your software will do that then from there it would seem possible to change some parameters like begin station (changes the spiral length) and run the station offset report again to see if your found points fit better, etc.

Also when first creating the spiral, if there is a point near the end of the spiral the software asks if I want to use that point and then it adjusts the spiral to fit that point if I want.

If you send me a point list I would be happy to run the points thru this program and send you a station offset report. Might be helpful or not.


 
Posted : November 10, 2025 12:57 pm

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