I've got a project with a ROW that runs along a state highway through an urban setting.
The highway enters town from the north, the speed limit is down to 30 mph 1/2mile before hitting a stop light, then a few blocks turning east at a big intersection with a stop light (west end of my east-west highway project), double turning lanes and a big curve through the intersection. The right of way is dedicated roads by subdivision.
DOT sends me a newish project (2010) with a bunch of information all in state plane with a scale factor. This was an improvement to the intersection and the road heading south so the north end of that project overlaps with the west end of my east-west project. I think great, that part of the right of way is completed. I look at the plan set and for my highway through the curve the 2010 project was dealing with the hard surface, no ROW monuments, no property lines except graphically.
And the curve is a spiral-curve-spiral. No chance it's centered in the ROW cause all the subdivisions are simple curves. I care of course about property lines, the centerline of the highway pavement doesn't have to be on the centerline of the highway ROW, and with 400' spiral lengths it sure isn't.
Still trying to process 400' spirals for a 30 mph road. Maybe an engineer can explain that to me.
They probably still designed for 45-55mph. Did they super elevate also?
No, it's a big nasty intersection, everyone hates it cause so much is going on. No one is speeding through there.
Folks that enjoy math will find a way to use it.
As a retired highway design engineer AND Land Surveyor, I wish I could give you an answer. I never understood the use of spirals on any design speed lower than 60mph, (maybe even 70).
Andy
From what I understand the Alaska Road Commission designers were former RR design engineers, and this is when the top speed of your average automobile was about 40 MPH. They would design spirals on every curve, regardless of it's delta angle and/or degree of curve, and all ROW was an offset from the centerline. They even had one in Juneau that was a spiral-spiral-curve-spiral (had to calculate that one, Civil3D couldn't handle it).
spiral-spiral-curve-spiral: Makes my head hurt just thinking about it.
I was so glad to get AutoCAD back about 1985, it had curve calculations and I didn't have to do those calcs for spirals anymore. Actually, the centerline calcs weren't so awful, it was offsetting it by hand that was such a PITA.
Real RRs have simple curves along the ROW and spirals for the track (might as well lay tracks out with spirals the force of the train will create them if you don't).
In this case the ROW was done 100 years before the 2010 design, so simple curves for that. How far off the centerline of the pavement is remains to be seen, probably about 1-2' so no huge deal.