Broken-back Curves

I'm not sure what a "broken back" curve is, but I assume you mean the short tangent between the two simple curves in your diagram.

My guess for the reasoning is to allow calculation of the delta. If they were compound curves and no delta (included angle) was shown in the drawing, then the curves may not be calculated precisely.

There is similar reasoning for reverse curves.

I have never heard of that nomenclature. Just seems like two curves.

I have never heard that term either. Looks to me as if it is two different curves just separated by a short tangent. See a lot of these at small scale on curb islands often a little half a foot straight line at the bull nose separating the two arcs. If they were together and the radius just changes I would use compound curve. Looks as if the radius in your diagram are parallel but the bearing in to the second and delta could identify that. Just saying you might see that on a test where a corridor two and some parts of each curve are given and one must solve the rest . I am just throwing that out. FYI hint hint.

I've always heard it used, and used, to reference non-tangent curves.

Reaffirmed by Wattles

I heard this term in school, but don't think I've seen one in the wild yet.

Maybe it's just a simple way to avoid a non-tangent curve.

I've always thought it was a common term for two curves spaced very close together but otherwise common curves with nothing else unusual. Much like rear corners of a subdivision being designed to be .30' apart, don't do it unless it is absolutely necessary. Instead of the broken back curves, find a way to make one smooth curve instead.

This is the situation I've heard described as a broken back curve....

I assume the PCC is point of compound curve but based on the diagram it's a lie? 😏

@KimBob I'm pretty sure I don't know what "Reaffirmed by Wattles" means. Care to elaborate?

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.