Broken-back Curves
I was intrigued by this verbiage and started digging around. So on the engineer side this term broken back is used I had just never heard of this before. Anyway it is frowned upon based on what I could find but sometimes they just do it anyway. I also found some training on how to take both of these two broken back curbs and for design standpoint make them into a compound curve so you might be getting into that which the math seemed pretty neat to do this and remove the tangent piece between the two
I recall the term from a route surveying course decades ago, but I don't recall ever seeing one on any plans in practice. If I can attach it, here is a scan from "Route Surveying" third edition by Pickels and Wiley (1951). It has a brief 1-1/2 page discussion.
I assume the PCC is point of compound curve but based on the diagram it’s a lie?
Point of crunched curvature
On pg 4-22 of “Writing Legal Descriptions” Wattles states that a broken back curve is merely another term for a non-tangent curve.
The diagram is not of a broken-back curve, as there is a tangent section between the two curves. Norman has it right...
After doing a little google search, it seems that engineers use term to describe two curves separated by a small section of tangent. They seem to be of concern when dealing with supers. As a surveyor, I was taught that the term describes non-tangent curves per Wattles.
On a side note, does anyone know if there is a PDF version of Wattles? I seemed to have misplaced my copy, not that anything has ever been 'Lost' in the mess I call an office.
So far I've only been able to tell that a "broken back curve" is an undefined colloquialism.
Others have posted that Wattles states that it is a non-tangent curve. However when I read Jon Payne's post that he found a definition like the original post I checked my Route Surveying text book (Meyer and Gibson) and found the same. So, it seems we have multiple definitions.
Personally I don't see why anyone would use broken back curve to define a non-tangent curve. If both phrases have the same number of syllables, where is the economy?
Colloquiallisms in general, are meant to make you sound wise, confusing or both.
"Colloquiallisms in general, are meant to make you sound wise, confusing or both."
I think we have different definitions of the word. Colloquialisms are just informal substitutions, so yeah the term 'broken back curves' is one. But I don't think it's used is to make anyone sound wise. I've only heard the term used between surveyors in conversation. Anything else, I use the term non-tangent curve.
The more interesting part of this thread is how our engineering counterparts use the term in a significantly different manner.
Personally, I use the term "broken back" specifically in cases where compound or reverse curves are non-tangential at their common point.
