1923] Proceedings of the Elisha Mitchell Society 33 



shades of tan. With the aid of Mr. I. V. Giles the para-cymene was 

 further explored. A new compound, 2-amino-5-chloro-p-cymene, was 

 prepared and many new dyes were made by coupling it up with 

 phenols and naphthols of different kinds by means of the diazo re- 

 action. Some of these dyes owing to the presence of the chlorine 

 atom are of especial beauty and brilliance. 



261sT Meeting — December 12, 1922 



T. F. HicKERsoN — Transition Spirals for Highways: a New Method. 



The alignment of highways consists of straight lines and arcs of 

 circles. At the junction of the two, there is an abrupt change of 

 curvature from zero to the full amount of that of the circle ; in other 

 words, there is a sudden change from a curve whose radius is infinity 

 (a straight line) to a curve whose radius is in extreme cases as small 

 as 80 feet. A transition spiral provides a gradual change from the 

 one to the other. It is a curve w^hose radius varies as the distance 

 from the point where it leaves the tangent to the point where it coin- 

 cides with the circle. Sharp curves should be banked, that is, elevated 

 on the outer surface ; and obviously this too should be done gradually. 



If the radius of the circle is larger than 500 feet, there is no 

 special demand for a transition or easement spiral so far as avoiding 

 a lurch is concerned, but spirals afford long approaches to curves, 

 and they therefore add much to the aesthetic appearance of highways, 

 as well as lessen distances ; this last advantage means many dollars 

 saved when designing hard surfaced roads at several dollars per 

 square yard. • 



In every case of a change in direction along highways, where ample 

 distance is available for long approach tangents, it is the opinion of 

 the writer that the most perfect alignment consists of two spirals 

 coinciding at the center of the curve. Where tangent distance is 

 limited, a combination spiral and circle should be used if possible. 

 In extreme cases, as in mountainous country, curves occur so close 

 together that only circles (widened at the center) can be used. 



The equations dealing with spirals are very complex and uninvit- 

 ing to the engineer in the field. It has been the purpose of the writer 

 to simplify the method of application to highway location, since all 

 the literature on the subject at present relates to railroad curves. By 

 the aid of tables compiled by the writer, spirals may be laid out in 

 several ways with as much ease as in the' case of ordinary circular 

 curves. 



