lugoben Nov 3, 2015:

philigoddard This information appeared in the context and you identified the Spanish document that had it. The English version of it is the one you don't seem to understand, but how can that be if you pinpointed the document and you must have understood what it said in Spanish. What I definitely know is that the context is not talking about transition curves or rail roads. Transition curves is as they say in Spanish "es harina de otro costal". It is not taught in a secondary school textbook.

Concepto.
Enlace es la unión armónica de dos o más líneas curvas o rectas y curvas entre sí, por medio de tangencias.
http://dibujotecni.com/geometria-plana/enlaces/

lugoben Nov 2, 2015:

bigedsenior The term requested and the context given is not making any reference to rail roads or anything of the kind. The text refers to a technical drawing textbook from secondary school. philigoddard provided a reference about the technical aspects involved in a Spanish reference and I found the English counterpart making the same definition as the Spanish context given. If you have a look and read the English reference given you will realize they are both talking about the same subject matter. I hope this clears any questions still persisting. Here is a definition for transition curves:
Definition
A transition curve differs from a circular curve in that its radius is always changing. As one would expect, such curves involve more complex formulae than the curves with a constant radius and their design is more complex.

bigedsenior Nov 2, 2015:

David, roads and railroads are only two of many examples of the practical use of transition curves.

lugoben Nov 2, 2015:

David Hello David, in the English reference provided there is complete coverage of the subject Technical Drawing with respec to Links(tangencies) which is a subject for secondary school math. I hope this is what you need.

David Russell (asker) Nov 2, 2015:

Is transition curve specific only to road and rail lines? This text book refers to technical drawing in general.