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.
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.
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.
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.
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. 😏
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.
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.
